@JorgeStolfi
Use an instance with much more than 500 Chars...
They are existing.
There are forked Mastodons outside, which can and have configures max character-size up to 5000 or more chars.
There are pleroma-Instances outside, which hast default 3000 or 5000 Chars i think. And many admins have set up the limit much higher.
There are forks of pleroma, with more allowed characters.
There is Friendica out in the Fediverse, which has NO limit.
There is hubzilla, zot, misskey... they all have more or no limit for characters in postings...
You can try them all. You are as connected to the fediverse, as with your actual mastodon-instance... don't be afraid to test other instances or even other software than mastodon...
And if you find an instance or software, wich fits your needs better... just move your followers and followings to this new instance. There are Howtos and Scripts for exactly this: moving your account to another instance.
@valhalla @jupiter_rowland @cstross @bitnik