Here is the procedure I used to replace a failed disk drive when the only available replacement was a same ID-name but a different volume-name drive (ID=2 aka dbk200)
Note that I had only one bootable drive with VMS 5 installed.
The issue - SYSTARTUP_V5.COM would freeze when attempting to MOUNT a drive with matching ID but incorrect volume name.
To get around the situation I initiated a minimal boot into the main OS drive:
>>> b/1 dkb500:
I needed to bypasses SYSTARTUP_V5.COM.
SYSBOOT> SET STARTUP_P1 "MIN"
This was enough to boot into DKB500 to get into VMS to edit SYSTARTUP_V5.COM without running it first. Unfortunately min boot also causes the VMS to ignore othet drives thus I could not yet change the volume of the new drive as VMS did not see it. I could though EDIT SYSTARTUP_V5.COM to comment out the line where VMS MOUNTed DKB200. With this complete I could get past the point where SYSTARTUP would freeze...Save/ rebooted.
VMS completed rhe boot. From the $ prompt I initialized (formatted) the replacement drive and changed the volume name to USER2 like the old one was called. Volume names are important in VMS SCSI and DECNET environments.
I next uncimmented the line in SYSTARTUP_V5.COM to again MOUNT DKB200. I made a few other edits related to MULTINET while I was in there.
Side note - One of my expansion units had a bad drive and one had a bad power supply. I swapped parts around. I now have a larger DKB200, and I also have a new DKB300 that I can use as a backup boot drive, should DKB500 fail.