I apologize for my terrible explanations, @BlakeTerhune!
My initial question was how to read one field and then apply a domain value to another field with UpdateCursor. (To be honest I had written successful code for this ... then accidentally changed something.) You helped immensely, which I very much appreciate!
After I applied your suggestion, I then attempted to update the code to search the OWN1 field for "ITC", and "TRANSMISSION, TAX DEPARTMENT", or "CONSUMERS.
It was supposed to search the OWN1 field:
If it found "ITC", or "TRANSMISSION, TAX DEPARTMENT", it would change the OpCo field to "ITCT".
If it found "CONSUMERS", it would change the OpCo field to "METC".
Instead, the code wrote only "ITCT" or "METC" in the OpCo field depending on which I ran first. I'm sure it's obvious that I'm new to coding (but unfortunately, I kind of love it), and cannot see what's wrong.
Hopefully, that makes sense! No matter what, thank you for your time.