Hello! I have a mess of pattern, and I must go choosing just a few notes that are mixed with others that belong to other instruments. I tryied to hold Control while selecting to go selecting multiple notes but it doesnt work. There's a way to select in this way? Theres any way to select using filters? (For example; select all in Channel 1 & 2 except all the ones that are F-3. Thanks in advance!
OpenMPT only supports a single rectangular selection, but it can span several channels. Just drag the mouse or shift-click in the pattern.
However, what you want to do may be possible with OpenMPT's powerful Find & Replace (https://wiki.openmpt.org/Manual:_Find_and_Replace) tool - as long as you only want to modify and not move those notes, it can probably do what you're looking for.
In addition to Saga Musix reply, you can also copy an entire block of notes, then search/replace within to remove notes.