[geek1011]

You won't have any issues which can't be solved with a factory reset with the OCP packages.

FYI, here's a small list of tools/mods and their safety:

Completely safe:
- Calibre/KTE
- Kepubify
- Covergen
- Seriesmeta
- Dictutil
- PyGlossary
- Custom fonts
- Custom translations
- Other external tools like these

Unlikely to cause issues, can be fixed with a factory reset:
- Newer Nickel mods (the NickelHook ones):
. - NickelMenu (but the cmd_* actions are more risky depending on what you do with them)
. - NickelSeries
. - kobo-dotfile-hack
. - NickelDBus (not released yet) (slightly more dangerous)
- Other readers:
. - Plato
. - KOReader
- FBInk
- KFMon
- MiniClock
- NiLuJe's stuff
- calibre-web sync server
- vlasovsoft
- Database/config modifications

Same as above, but touches system files directly:
- Kobopatch (Nickel, most libnickel and other patches)
- Manual firmware upgrades

Possible issues, but fixable with a factory reset:
- Kobopatch (some libnickel patches, specifically ones around syncing and the home screen)
- Telnet/SSH (but it depends what you do with it)
- fmon
- Kobo-UNCaGED
- Non-trivial LD_PRELOAD hacks
- Skipping multiple major versions when doing firmware upgrade
- Using firmware from another hardware revision (just the KoboRoot.tgz)

More dangerous, may cause more serious issues if they fail (possibly unrecoverable on devices with soldered memory):
- KSM (on older devices/firmware versions)
- KoboLauncher
- Night mode
- KoboCloud (by fsantini)
- Older software/mods (i.e. before fw 4.x) (on older devices/firmware versions)
- Anything touching the init scripts (busybox, rcS, u-boot, pickel)
- Anything messing with mass storage mode
- Anything dynamically modifying system files
- Older telnet/ssh hacks (i.e. not built-in or part of one of the tools in the above lists)
- Large firmware downgrades without a factory reset
- USBNet
- Custom kernel modules

Same as above, but not really hacks:
- Opening up the device physically
- Full factory reset (this is actually somewhat of a fragile process, so don't do it unless you have to)

Highly dangerous:
- Android
- advboot
- KSM (on newer devices/firmware versions)
- Older mods (i.e. before fw 4.x) (on newer devices/firmware versions)
- Kernels
- U-boot
- Screen replacement
- etc

P.S. Sorry about the lack of formatting in this post, I was typing it from my phone.