Need to remove the Time Machine Partition from an external hard drive

Generally in order to reclaim a partition and include that capacity back

into the whole, you'd need to reformat (erase/format) the hard drive.

So the need (if present) to save anything from there, should be done

ahead of this action; as ALL of the drive's contents would be wiped.

Usually a user would try & keep more than one backup option, including

system clones (these can boot & run the mac) and other copies to keep

safeguard information until you've found its usefulness has tarnished.

The 'disk utility' can be used to erase/reformat an attached storage drive.

Good luck & happy computing!😊

You can copy a TimeMachine backup by dragging the backups.backupdb to another hard drive that has been partitioned as GUID and formatted Mac OS Extended (journaled).

My only concern is corrupting the existing backup file; I understand 
that time machine backups are hard on the drive (meaning don't last 
long).

No reason to believe that's true. The TM drive probably isn't being used any more than your computer's hard drive - keep in mind TM only works when there have been changes to your computer's hard drive. At work and home I have large TM drives which are storing more than 3 years worth of backups and have been in use 4-5 years. Actually now that I think about it, my 6 year old home iMac is using the same TM drive that my previous Mac used.