Easy enough to do on an old but still virgin phone, the only pain was cleaning it up enough to get a new seal on.

Pulled the back off with nothing but methanol, suction cup and a spring steel spudger.

Honestly buy a spare back with pre applied seal from the usual suspects. If you're doing repairs for money and time is important then don't be scared to shatter the back glass. Let the customer know just in case they don't like the pricing.