is there a way to refederate instances just for me?
when I see that whichever instance I choose is defederated from another bunch of random instances, is it possible to have those show in my feed without making a separate profile from other instances? and can I turn them off again if I see that defederating was the right idea?
You could host your own instance, that way you're completely in control. I'm also doing that, just because I don't want people(mods, owners) to decide for me who I interact with or not.
Yes, but It's pretty hands off since 99% of security stuff is managed for you by the Lemmy software, including rate limiting. Just make sure you use a secure password and if you want put the instance behind cloudflare which is super easy to do.
If the instance defederates, users do not have an option to interact with the defederated instance anymore. The only choice you have then is to join an instance where the moderation policy agrees with your values or host your own instance. If you just want to see if defederation was the right idea, you could just visit those instances directly and look at their local timeline.
You can just go to that instance's webpage and view their frontpage. It's worth noting that NSFW posts are often hidden without an account though, so if an instance was defederated for NSFW content it might not be obvious why.