Yes the update comes only to btu.
During beta testing I had my motherboard replaced and CSC changed as well (sadly)
I simply flashed (still during beta test) the official BTU firmware then updated again via OTA to beta version as my serial number and imei remained the same.
So I didn't have any problems going from last beta to official 7.0 release.
But as you had your whole phone replaced I think your imei and S/N are new ones. I believe that if you find have BTU beta at the moment (you mentioned XEU UK/IRL) you can't get early release of official 7.0
But I might be wrong.
What I would do in your case is
1 flash official beta BTU with Odin
2 update OTA to latest beta or possibly straight to official 7.0.
Official 7.0 is BTU so it won't update via OTA from XEU.
I'm beta tester as well.
But my CSC is BTU.
As far as I was aware beta version of Android 7 was only BTU not XEU.
If you had BTU CSC before and after replacement it changed to XEU it might be worth to speak directly with Samsung. BTU and XEU are sort of the same but beta applied only to BTU.
If your phone when bought had a BTU CSC I would email them.
Either through official email or beta team.
Here's email to beta testing team.
I asked the question and it looks like XEU updates are at least a week behind so I flashed 6.1 BTU MM and I now have the new 7.0 software. However, if you flashed you loose the galaxy beta programme app and if you get it, it won't work.
Samsung members app bug.
Other issues I found so far are:
- camera stabilization causes vertical shaking when using QHD
- Spelling correction still poor (English language)
-icons names errors
New line should start with consonant.
Not with vowel.
Error doesn't appear when icons are grouped (kind of folder on app screen)