I imagine that Belarussian folks will love having less trained, less motivated, and less disciplined Russian troops occupying their territory for the winter. The foraging will not win Belarussian hearts and minds, I'm sure.
When the Russians mass in preparation for crossing into Ukraine again, will Ukraine shoot artillery across the border to start atritting the Russian formations before they cross, or will they wait until they are on Ukrainian soil? Waiting would give Russia the advantage of deploying their forces into less vulnerable formations. Hitting them in Belarus might bring Belarus into the conflict. There are some operational challenges there for Ukraine.
I'm sure that troops massed in Russia near the border would draw Ukrainian fire well into Russia, since they are already involved, so I don't think that Russia will attack in the Kharkiv-Sumy area. But I'm a broke-dick old Marine enlisted man. What do I know?