Referring to How do we want to handle the old questions that got obsoleted by the IOTA Chrysalis update? and https://meta.stackexchange.com/a/191984/, we'd like to have a custom post notice on the IOTA site:
This question is about an obsolete legacy IOTA protocol that is no longer used on the IOTA mainnet. Its content is preserved mainly for historic interest. If you are interested in how this is handled in the current IOTA mainnet, search for similar questions or ask a new one.
I am aware that only we mods can add those notice, but others can tag questions with https://iota.stackexchange.com/tags/legacy-protocol/info and I'll probably do a search for them regularly to add the post notice. Or you can use custom flags.