Repartitioning a HDD A pal has an external, 1TB, Glyph HDD.
It has two partitions; one has his Time Machine backups &amp; the other has a clone of his internal HDD.
He is running OS Mojave.
His plan is to purchase another external HDD, erase the clone of his internal HDD from its current partition on the external HDD.
What he is trying to determine is if, using using Disk Utility, he can go to that partitioned external HDD and resize it so he can use it in its entirety for his TM backups without destroying/harming the TM backups currently residing on the other partition of that HDD.
I did this.  I had several partitions on my external hd that I had the time machine partition.  I deleted the partition after my time machine partition. I expanded my time machine partition.  All is well. 

I'm running 10.l0.5.

He may consider cloning his startup drive to the new hd before erasing the old partition.
R