Mitch said:
I believe if you want a dev version you have to compile it yourself.
Mitch is correct. Compiling MESS (for Windows at least) isn't the easiest thing either 'cause it uses bunches of tools and libraries, which seem to change from version to version, from various places. There are also multiple "how to compile MESS for Windows" webpages out there of various vintages. (And, you guessed it, the older instructions are incorrect for the current version.)
But once you get the compile working, it isn't too hard to make changes. (Although re-compiling does take some time.) Some logging statements are also commented out, so you want to edit the source (or even add your own logs).
You should also know that the logs are no-where close to something like Z26.log (although they can be just as big :-) ), and IIRC only cover some MARIA stuff.