Mastodon doesn't provide any setting to change:
- the number of characters in posts
- the number of pinned posts
- the number of characters in bios
- the number of fields in a profile
- the number of characters in the display name
- the number of options in polls
- the number of characters in poll options
- the upload size limit of images
- the upload size limit of videos
- the upload size limit of audio
- the accepted upload file formats
- the number of search results
- the number of trending hashtags
- the size of local or remote emoji files
All those settings are hardcoded in Mastodon, and changing those would require altering the code and recompiling Mastodon assets.
As mentioned in Mastodon version and code changes, no code changes are supported on Masto.host infrastructure.
Everyone hosted on Masto.host shares the same base code, and running the unchanged code is the best way to automate upgrades and maintenance. Sorry.
If Mastodon ever offers a setting to change any of those (like they do for other settings), Masto.host will fully support it and provide a way to adjust it to your liking.