What if the USSR of October 1925 is ISOT'ed 20 years in the past?

They could try. Some of it is a matter of which side figures out what is going on first. It seems to me the Soviet side will have an easier time figuring that out. That also means they will have an easier time using preparations and trickery to defeat the other side.

The USSR could also unilaterally cede independence to the Grand Duchy of Finland if, for example, that can get them Scandinavian neutrality, and neutralize Tsarist troops there, if there is a grand coalition forming between Germany, Austria, and France against the the revolutionary state.



This is a a good point, they would have very valuable knowledge. Especially once they start communicating and once larger events make it clear they should be believed. At the same time, the Soviet state and Chekha are pretty good at controlling and locking down internal movements, and may very quickly make non-repatriation and control of foreigners communications a priority. I think a few would almost certainly escape though due to security services sloppiness, corruption, and their own ingenuity.





All true that there are masses of old regime troops on the western fringes in particular. At the same time, these forces as of late 1905 exist in a certain state of precarity. They've been holding back revolutionary disturbances since Bloody Sunday at the beginning of the year, and enduring mediocre to bad news from the Far Eastern front. In the interior, they've be fighting against peasant rural land seizures, jacqueries, and banditry. In Poland, they are holding down nationalist and industrial unrest that would persist in OTL for another two years.

The Soviets have a lot of angles to work and exploit 'contradictions' and differences between downtime actors to weaken or neutralize their threat. For example:
a) Put diehard Tsarist troops in Poland-Lithuania "between two fires" by supporting, even if only momentarily, Polish independence aspirations
b) Alternatively, appeal to Tsarist troops Great Russian patriotism by advertising the Soviet Union as "the only Russia you've got" in the face of disloyal ethnic minorities, Poles, Jews, Balts, Romanians, Finns, who want to break Russia up.
c) Divide Tsarist soldiers from officers by telling the soldiers they are already late for the division of the estates, they are released from military service forthwith, and welcome to claim some land to farm on their own or with family members while there is still some around. Our Soviet bureaucrats will help! And this can be reinforced by possibly sending some people or family members from the NEP era Soviet Union to the uptime/downtime border with bullhorns (or through letter communications, "high this is your mama, the government taught me how to read after the old regime got you killed in the next war") to ask their younger selves or family members, alive or deceased, to "come home".



Probably so, the truth, in general terms, wasn't really hidden so it will likely get out. Even though they could try making stuff up, like "we sent them into exile" or, "they became anonymous private citizens".



Yes, the denunciation of imperialism wouldn't sit well with anyone. The default on foreign loans wouldn't sit well with any foreign creditors, German included, even if they'll have a schadenfraudenlich laugh at French expense.

The trick will be physically accomplishing this in the face of opposition by the Red Army and Red Air Force.



Except inasmuch as it worries about excessive unilateral German gains, but yeah, France is ill-disposed to Russia, and its foreign policy premises and financial markets are a shambles.



I don't know if Soviet citizens were finding it that disorderly by 1925. Perhaps culturally unnerving. Upsetting for the religiously conservative.

Russia is demographically battered compared to 1914, but its military is higher tech and tactically knowledgeable. It has more machine-guns and submachine guns per unit of soldiers than the 1905 armies and definitely more tanks, tankettes, and motor vehicles, and has expertise in combat use of armored trains. None of these are up to the standards of the 1930s, and are not particularly impressive by 1925 standards or even 1918 western front standards, but this is 1905, and its a good tactical edge to bloody the enemy in any early encounter battles in 1905. Also, the Soviets have an Air Force capable of air to air actions, bombing, rudimentary close air support, reconnaissance. Again, a primitive Air Force by 1918 standards, but a frightening thing for any 1905-1908 army to encounter.



That's the fear the Soviet regime would try to stoke.



If things work out "just so" for the CPs, where they "kick in the door", and the "rotten Bolshevik edifice comes tumbling down" or gets maximally Brest-Litovsk'ed [and I've outlined potential obstacles to it], and tech is discovered, while the French and British are hostile to Soviets bystanders then I suppose war is put off for now, but Britain and France and possibly the US are going to be getting very worried about the world balance getting knocked out of whack. At a minimum, I think French-British ties and strategic cooperation will tighten. The Japanese on the other hand, would gleefully exploit the difficulties or downfall of the USSR to the extent they could, and get comfortable making policy choices increasingly independent of Britain. Some possible parallel anti-Soviet moves between the CPs in the west and Japan in the east may lead to more synchronization of policy between the two, and US-Japanese tensions might rise.

Changes WW1 very severely. America is going to be much less isolationist with a very powerful communist neighbor that has a superior navy and actual airforce.

Sun-yat-sen is happy since the Soviets would aid his development of China. One of the very few nations to benefit.

The Mexican Revolution becomes the Spanish Civil War of the 1910s. Pro-Soviet elements in Mexico get Soviet aid which allows them to win the civil war.