...bump...

Any word on this since 2013? I have a need to do this as well.

I'd like to un-manage old devices not seen or heard from in some set amount of time but keep them in the JSS for their inventory records. I don't want to delete them and because I can't find them, I can't un-enroll them. I've now got a heap of them I'd rather not do one at a time manually.
I'd vote for this.

Your best bet is to get a smart group together of enrolled devices and then do a mass action from that.

If you do some sort of buyout you can mass upload a list of devices present in a CSV to a static device group and then target that static group in a smart group. The MUT would come handy in this scenario.

If you want to unenroll devices that haven’t checked-in/updated inventory in “X” amount of days you could do this with a smart group too.

Had to do something similar to track Macs successfully migrated to our new Jamf server:

Take the desired endpoints, get their hostnames/Serial numbers in a comma-delimited format (using Apple Business Manager's search field or delim.co), then drop them in the Jamf Pro search box and do a mass action: Edit management account and set the fields blank. It took a moment, but the 175 Macs I wanted to target went from Managed to unmanaged. And confirmed in the Managed/Unmanged counts.

Update, I don't think this works with LAPS enabled. Since upgrading to 10.50+, this method of bulk unmanaging no longer works.