Does changing mining algorithm(SHA256) of bitcoin cause any side effect?
Apart from GPUs being more viable for mining, no, there isn't. (And asics being less viable, or more or less useless..)

Apart from maybe a difference in difficulty etc, but blocktimes and blocksizes should be the same.

(Unless ofcourse they changed it in the hardfork itself, but that has nothing to do with the mining algorithm.)

EDIT:

Note: I've answered this question in technical terms, not economic/emotional terms.