The one thing I really liked about Mach was being able to type in a tool number and go. UCCNC does not do that and from what I understand the way Mach was doing it wasn't the best method overall. T# and H# are separate items.
Like me you are using fixed length tool holders so I assume you are not touching off after each tool change.
Typing in g43 h50 in the MDI goes pretty quickly if I am doing one off work. I now have an ATC on my knee mill but before that I would do the tool changes in code with no M6 commands. I program in where I want XYZ to be for the tool change and use MO and G43 H##. Here is an example.
Machine is running with a tool in it:
M05
M09
G00 Z12
G00 X4 Y7
M0
(change tool push start)
G43 H50
M03
M08
Continue code.
The nice thing about doing it this way is you can put the machine where it needs to be to change that particular tool as opposed to a M6 macro that is going to send the machine to a fixed place.