Does anyone know whether the Acashiea Moca vampire companion mod works with MCA 7.0? I downloaded this because MCA does not contain any vampire companions, and it's suposed to use the MCA 5.2 scripts. However, I'm not sure how much the companion scripts changed between the mods and, if there haven't been any changes, I have no idea how to change th dependency from MCA 5.2 to MCA 7.0

I've no idea on the compatibility between the two. You can use Argent's http://mw.modhistory.com/download--5258 to change the dependency (you can also use Wrye Mash or MWEdit or Enchanted Editor or... But from what I understand TESDTK is simpler to use).

What you may find is that the companion mod refers to scripts which were present in v5.2 of MCA.esm but have been either renamed or removed in the latest version. In that case you'll get some errors on attempting to start a game. To fix that you'd need to edit the companion mod, either duplicating the removed scripts or changing the name to match the renamed script.