changing valuation class at plant level

Hello Guru's

I want to change the valuation class assigned to a plant since it was assigned a wrong valuation class.

If i want to do so what would be the impact? (i have a list of GL accounts which are different in both the valuation class).

Also the plant was created 6 months back so how do i check if there were postings made already on this plant and what do i do with them?

Thanks