I wonder how I could modify, compile and run it in parallel besides the Debian repos version, any tips?
Clone the source from Git and run `autogen.sh --prefix=$HOME/wherever/you/like`, then `make install`, then run it like `$HOME/wherever/you/like/bin/geany`.
Besides, how do you guys handle the GUI part of Geany? It seems they are coded directly and without any visible aid like Anjuta or the like.
It's a mix. Most of the GUI is done using [Glade](https://github.com/geany/geany/blob/1.31.0/data/geany.glade), but there is also some (too much) which is just hard-coded.