yes it works, but be sure you have FS version that matches yout main firmware version. otherwise instability may occur.
for w810i for example, if you have a R4EA031 main you can flash a R4ED001 FS BUT generany speking both versions should be the same = R4ED001 for the phone to work correctly. so this w810i is only a particular case in which flashig different version work without any trouble at all.