20w50 is fine to stick with or run in that engine, in your climate. So is everything down to a 30w. The cold start thing is usually very very overstated. Somewhere there is a Toyota oil viscosity guide for your engine, from a market other than US or Canada, and it will show a range of viscosity that you can run successfully, which will include 20w50. So, while you didn’t know what you didn’t know, it amounts to exactly zero effect in this case. If it were mine, I would not change anything. It would be nice to see a million mile Toyota running nothing but 20w50 its entire life.