Yes. Just follow this .
2 points though (and in that link)
- If uefi, do the extra 2 commands in [Addition UEFI commands]
- If bios-legacy, when you do 'grub-install /dev/sda'
make sure sda is the primary drive (the mbr one). If sdb is the primary drive, do
If unsure, you can do all
But if you want to be sure, verify primary drive with one of these many commands
sudo parted -l
sudo fdisk -l
It needn't change. Why would that be changed?
Aha! That's where you got the drives wrong. As above, check primary drive (mbr) and do as appropriate.
Just to check, Isn't your fstab in UUID and not '/dev/sdx'
And grub, it is already in uuid. Where it states set root=(hdx,y), it will be superceded by search line and that is in uuid . Unless you intentionally set grub to use /dev/sdx (you can disable uuid in /etc/default/grub, but that's only for ....er, fools (cannot put it nicely, I tried).
And what (where) else would the system (not user) not define uuid so it gets the partitions (eg Debian/Windows) wrongly? Any more places?
 grub uuid - set root=(hdx,y), that's to make the bios search faster instead of going through all the UUID's in all the partitions (so we can boot faster). There's also the 'hint' to make the search faster. These can be wrong (but must be valid ) and if the search line for uuid is correct, it will boot correctly. Long story, I can still go longer, if you wish.
 -need explanation? Ask. Another long story.
Further explanation - Regardless of how many drives you have, there is only one primary drive.
And that is also true regardless whether you booted up Debian, Windows or Manjaro and where these are located. I think this is where you confuse yourself.
Confucius say people who are confused should have only one drive.
Confucius also say she who use many drives, one for each OS, so not to be confusing, is going to confuse herself.