Thanks, as usual, for the quick response!
So, if I understood, I actually can add new Custom Forms to old tickets, but so I have to do it manually on each ticket via the Manage Forms button.
Since I still don't manage hundred of tickets, it seems like it works for me. Otherwise, I'll use currently Custom Form adding the necessary new fields.
Solved 100%
Thanks a lot.
P.S.
Is there any tentative date for 2.0 realease?