Compile

# cd /usr/ports/x11/dwm
# make fetch
# make patch
# edit /usr/ports/pobj/dwm-...
# make install
# make clean

Installation steps

- I copy them to local ports tree
- make extract
- do changes in source
- make build
- make update-patches
- make clean patch
- make package

Download the port sources and patches

$ make patch

Go to build directory

$ cd $(make show=WRKDIST)
*modify what you need*
$ cd -
$ make reinstall

next time first do

$ make clean=all

make a patch with your changes

$ diff -u