The same subscription is often reachable as both a playlist and an Xtream account, because the panel builds the playlist link out of the account. Adding it as Xtream credentials is strictly better: you get the same channels plus movies, series, the provider guide, catch-up and an expiry date, and the desktop app keeps a local catalog so the source opens instantly next time.
Stalker portals are the exception. A MAC address is a different identity mechanism, and a portal cannot be expressed as a playlist or an Xtream login. If that is what you were given, the Stalker form is the only way in.
Switching later costs nothing: add the better source, check that it works, and remove the old one. Favorites and history belong to the source, so they do not carry over.