Is there a way I can have OPENMPT play a sample at its base frequency without having to change the note transpose option in the sample editor menu every time I map a sound to a note that's not C5?
Please elaborate a bit more what you want to achieve and what state the samples you are in that you want to play. Are the samples playing at their intended frequency when played at middle-C in the sample editor, and you want them to map to different notes of the same drumkit instrument? If that's the case, you can right-click the instrument's sample map (https://wiki.openmpt.org/Manual:_Instruments#Sample_Map) and choose "Map all notes to C-5", which then causes all notes of that instrument to play a C-5 of the associated sample. Note that the context menu entry will always contain the note of the last selected row in the sample map, so if it mentions a not different from C-5, then you first need to enter C-5 into the first column of the sample map.
Oh, I see now. I didn't realize you have to right click to make the sample map to make the "map all notes to C5" option appear. Thanks for the help.