No unfortunately you cannot..

Easier and cheaper to make your own

Actually, a few years ago, I did the maths, and homemade ones aren't actually that much cheaper when you add up all the consumables. They are most definitely not easier. I found the reliability and time saving of the precast gels easily worth the small extra expense.

no

Of course you can.

https://www.jove.com/video/3465/pouring-and-running-a-protein-gel-by-reusing-commercial-cassettes