I want to register my X3 on egosoft to get the bonus pack but can't find the registration # in any of the files.

I tried to download the bonus pack and could do in without having registered my game there.
However, if you still want to register your game there you could contact GOG.

It says on Egosofts forum that for X3:Terran Conflict and later games you need to register on their forums to be able to download the bonus package but X3:Reunion and earlier do NOT need that.

I guess one needs to contact GOG.

EDIT: Now what is the "mod support patch" in the download section for X3:Terran War Pack? Would this one not be the bonus pack? If so, problem solved.

I tried do download them again and I could download X3 TR's and X3 AP's "All In One Bonus Package"without creating an account and activating my games there.

I meant maybe it already is on GOG so no need to go offsite but alright if you are all good.

I don't think so since the changelog mentions some changes for the Mac version which are better mod support for the DRM free version. Therefore, I think that the "Mod support patch" does exactly the same just for the Windows version.

No additions, official or otherwise, are included with the GOG versions of X3, X3TC and X3AP - they only contain the base games patched to the latest versions. The official Bonus Packs you can freely download off the Egosoft website work without any issues though on top of the GOG installers.