trans on mt63
You don't say which program you are using, which isn't helpful. I
suspect from your comment that you mean the IZ8BLY MT63 program. If so,
simply type '*' (a single asterisk) into the TX buffer before pasting in
the text. The same works for hand-sent text. The transmitter will then
start only when you tell it to.
It would be a good idea to read the help information for your program!