Are there any mods for this game?

                
A lot of them!
I'm using these:
https://forums.pokemmo.eu/index.php?/topic/74184-mod-shuffle-icons-mod-30-unovasinnoh/
https://forums.pokemmo.eu/index.php?/topic/100899-mod-generation-5-follower-sprites-v20-updated-for-2019/
https://forums.pokemmo.eu/index.php?/topic/56376-mod-hd-items/
You can also check out these:
https://forums.pokemmo.eu/index.php?/topic/99274-mod-moemon-enhanced/
http://www.mediafire.com/file/il4vcixq691sp8l/3DS+Pokemon+Icons.mod
https://forums.pokemmo.eu/index.php?/topic/104781-modandroid-compatible-pokemmo-hq-music-overhaul-v10/
https://forums.pokemmo.eu/index.php?/topic/100899-mod-generation-5-follower-sprites-v20-updated-for-2020/
Themes (go into the theme folder):
https://forums.pokemmo.eu/index.php?/topic/100408-gui-gen5-inspired-theme/
https://forums.pokemmo.eu/index.php?/topic/119678-gui-dark-theme/
You can find more there, but a lot of them are going to be outdated, as the game is still in development: 
https://forums.pokemmo.eu/index.php?/forum/33-client-customization/