Short answer: No.
/e/OS contains /e/'s fork of MicroG, built by /e/ and signed with their key. So it can only be updated with a newer version that is also signed with /e/'s key. In practice, this means that you can only update when /e/ ship a new ROM build containing an updated version.
If you want the latest, non-forked version of Microg, you would have to flash a different ROM