@Tandrael
Uninstalling seasons then installed it back in when you find it convenient sounds a little bit cheaty, sorry nope can't do that. Why don't you get the "immune to heat" and "immune to cold" lifetime reward? The game always start in summer, so you can get the heat one first then buy the cold one later, its only 10,000 LTR points.
Or you can set the game to all year summer and play your dynasty in only summer, you can just buy the "immune to heat" LTR. If you are worried about your gardening plants not blooming, then setting the seasons to summer all year long will be best.