One request I've had quite a bit for EchoFeed is to be able to handle specific, known usernames, between Mastodon and Bluesky where they are different (which is almost always the case). Some pastry-themed apps already have something similar but for EchoFeed it needed to work differently.
For EchoFeed, I've gone for the simplest solution which is also the most flexible - straight string replacement. "Replace THIS with THAT", or in real terms, "replace @robb@social.lol with @rknight.me when cross posting between Mastodon and Bluesky. Maybe you want to replace utm_source=mastodon with utm_source=bluesky because you're a big Business™ boy or replace every mention of "Twitter" with "the deep fake porn and hate platform" because you understand you don't hang out at Nazi bars no matter what. You can replace literally anything, it's up to you. The documentation has a bit more information about how they work.

EchoFeed won't replace strings in links and has the option to only do case-sensitive replacements. Replacements is an EchoFeed Pro feature and is available now.