No it doesn't force a spell change on them - it highlights spelling mistakes and gives you an option of - however many you choose - so many words which you can change it too.
If it is a word you use a lot - and you know ppl will understand such as vbulletin there is an "learn" option - and in the spell_admin.php there is an add option to add more words.
there is a working version on my board.
http://clanantivirus.com/forums/ if you wish to check it out.
and attached is a picture of the spell check window