Thanks for the answers.
I got some valuable info, I understand that forks are mess, but the situation I was talking about (which I didn't mention in initial post) is that particular coin is doing forks anyway, I mean they require everyone (users/ miners/ exchanges) to update to new version, old version stops working, there is some kind of snapshot of all transactions created and they start from that, old transactions are not included in new blockchain, just wallets/ addresses that held some amount of coins.

I have also new question, if no one replies I will create new topic, no worries: is it possible to block certain wallet/ address from spending coins?
There are number of wallets that should not be touched for some reason, my thinking is that if everyone updates their client (wallet) software you can blacklist those addresses so miners won't include transactions from these addresses in blocks, is that correct? I'm talking of less than 100 addresses, so I don't think that would "eat" much of processing power, I can think that blocking hundreds of thousands addresses would require some sort of database and heavy modifications to wallet, but with such little number I can't see a problem, am I thinking right? Thanks.