This has been requested on the forums: http://forum.openmpt.org/index.php?topic=3186.0

Now that transpose has been moved to a sub menu, it might be possible to add a "other amounts" menu item without cluttering the menu too much. I'll think about it.

Thanks Saga for considering it - I do think it would be a very useful feature - thinking about it a bit more I reckon values between -4 and +4 would be more than enough.

I thought more about adding one more menu item which would bring up an input box in which you could just enter the wanted amount - that way, we can do justice to every tranpose amount - you say that you want +/- 4, the next person wants +/- 6, and another person wants +/- 13 - now if we follow that logic, we'd come up with a menu with dozens of entries, that would be quite cluttered! A simple input box should solve that problem, and the most usual transpose amounts (1 and 12) will just stay there for convenience.

I think what you are proposing would be great and I take your point regarding trying to please everybody!

Finally got around implementing this. You can now select a custom transpose amount from the context menu or through a keyboard shortcut. Please try http://sagagames.de/stuff/mptrack.exe

That's very useful - cheers saga.

Just asking if this feature will appear in some future official version of MPT?
One other thing I thought of that would be even cooler was if this feature was in the same kind of format as the amplify button with an arrow box to click up and down to the transpose value you require - just a thought!

Well, it is already available in the test builds, as linked above. It will of course also be available in the next official build, but I'm not sure yet when I will release that. Since a few critical bugs have been discovered lately, I might actually make a new release next weekend.

same kind of format as the amplify button with an arrow box to click up and down to the transpose value you require

No Saga it's me who missed the arrows!
I'm sure they were'nt there when I used it.
Trip to the opticians for me I think!