You can change the notation resolution using the Notation Options button (beside the green lead sheet window button)
At the very left top of the window is a check box for triplet resoltion.

This will set ALL of the note locations to triplet, so turn it on when you move to 6/8 and off for 4/4. Any note you add in triplet will sound Triplet but may show as 16th without the resolution change. It will be correct, just be presented weird.

So unless you need to show 16th in the 4/4 section, just print in triplet for the whole song


BIAB for Windows Version 2019 (643)
Windows 10 (1909)