Well, Tsarist Russia
already had an appetite bigger than its belly. Congress Poland was a liability, and every Balkan adventure after the 1830s ended badly, sometimes very badly. I'd advise making them stronger through, as Eurofed suggests, domestic change to reduce the enormous social strains that industrialisation put on the fabric of the state; and also by making them
less adventurous.
Of course, it all depends on the PoD. Technically "Tsarist Russia" existed continuously from Ivan Grozny to Nicky, meaning that "Tsarist Russia" could be just about anything; on the other hand, the "ideology of Tsarism" was anticipated by Nicholas I and codified by Alexander III.
I'm myself rather fond of Napoleon winning as a PoD to start benefitting Russia, myself. The good ole' no-Spanish-ulcer-no-1809-war-Russia-less-bold-stays-quiet-another-year-Britain-forced-to-make-uneasy-peace jazz. This leaves a Russia without Congress Poland, which is good news for the Russian state: no constant revolts, no PR troubles complicating some alliances, no fears of Polish revolution for any *Bismarcks to exploit in using Russia for their own ends, and perhaps a somewhat more credible position as big brother of Slavic peoples; and for giving up what? Poland wasn't of any economy importance to Russia until after industrialisation, and without it, the capital will still exist, but will go to Donbas and other less vulnerable centres.
It also leaves Alexander I in a better position to realise some of his liberal ideas. As Eurofed suggests, you might want to adjust his personality as well - which is not really difficult, since he was so disordered in the attic, and no war of 1812 by itself divests him of the troublesome messiah complex.
Then, without the influence of Metternich, soften the swing into reactionary authoritarianism. Wilno university stays open, and *Decembrists can discuss their ideas relatively openly as long as they don't do anything too silly.
When Alexander I dies/runs away to Taganrog, Constantine will not have discredited himself by advocating peace with France, and more importantly will have had no opportunity to become a pseudo-Pole. Might want to throw Nicholas I under a carriage, just to be sure, however. Tsar Constantine, though rather eccentric, could maintain a cautiously liberal Russia. For convenience, lets give him a long life, because after him we may have to start making Tsars up.
Building on the work of a somewhat more energetic Alexander I, he could give Russia clearer nudges in the direction of abolishing serfdom - it's hard to do this
so much earlier because of the enormous power of the aristocratic interest, but a more gradual process starting earlier can only help.
The end of it is that, with luck and consistantly liberal politics, Alexander II's sketches of a duma may come into existance in the latter 19th century. It will be a body representing the aristocracy and miniscule middle class, of course, but it's
some sort of pressure valve for a state where historically throwing bombs was just about the only protest you could lodge with the general state of things.
Meanwhile, differant intellectual development in the more liberal climate. I would hope to see a
little bit more equality and integration for Jews. Alexander II's policy was contradictory: he wanted to make the Russian Jews as Russian as German Jews were German or French Jews French, but he shrank from anything that would require letting them take jobs or school-places from Christians. No real way around this, but we can avoid actual state-sponsored pogroms and start to let some more Jews into the respectable middle classes.
Also, differant development of the Ukrainian movement: for one thing, the climate will in general be more liberal and tolerant. For another, pan-Slavism will probably remain a more airy-fairy ideal. For a third, rather than 1863, which made the authorities paranoid about supposed Polish stalking horse nationalisms, you have no Poland in which to have a Polish revolt, but lots of Polish aristocrats. In other words, the
dastardly Franco-Catholic fifth column!!
!
Without an 1831 rising, there is no definite "we are abolishing Greek Catholicism" moment, but the Uniate church was splitting as it was between senior clergy who retreated to the Latin rite and congregations returning to Orthodoxy: let's say this trend continues gradually. We may end up with a situation where intellectuals who go out to study and cultivate the East Slav vernacular of Ancient Little Russia are considered to be doing the regime good service. Create the climate of later Soviet Ukraine - you can absolutely speak and publish Ukrainian (Little Russian) and celebrate the Ukrainian (Little Russian) way, but seperatism will not be tolerated and you do need to have Russian because, you know, everybody needs a job - and the problems of Ukrainians and with it Belarussian nationalism largely evaporate.
When industrialisation starts, fuelled by foreign capital, we've created a state in which the developing middle-classes can have their voices heard, the nationalities are more appeased, the Jews are less subject to persecution, and the landowning interest is marginally less powerful. We'll still want to avoid losing any wars for a bit, but such a state can avoid revolution and survive its social strains, and by the WW2 timeframe, it can put a respectable army in the field.