Yes, definitely. You don't even have to root the device. Copy it into /mnt/ext1/applications and it will show up in the Applications menu. You can build E-Ink capable applications using the SDK and install them (I recommend sergeyvl12's version of the SDK). You can also take utility programs from the Debian ARM distribution that LoneTech provided for running under qemu on a desktop system and run them on the Pro and 360+ devices. The devices also have a shell via BusyBox, and you can run scripts on them via Applications or the poterm application. You won't have root privileges (unless you run the get_root app under one of the older firmware versions), but you can do a lot without them. paola maintains a collection of useful information found in this thread:
https://www.mobileread.com/forums/sho...d.php?t=119973