I don’t see why they would decline transmission service if it is under warranty or if it is preventative maintenance on the 8 speed transmission (especially considering new trucks are still getting the 8 speed). If the educated consumer is aware that transmission fluid exchange (drain/ fill, filter & gasket replacement) is recommended at 30K intervals, they should honor the request.
The filter replacement is not part of their procedure and needs to be requested.
Monitor for leaks after the work has been performed, because the mechanic may have over-torqued the transmission pan bolts, which could lead to a failed gasket & leak.
If you come to them with a 100,000+ mile car or with transmission issues (which has not had regular service transmission service), I wouldn’t be surprised if they decline or recommend against the service. Otherwise, they may be held liable for a transmission failure after it has been serviced.
I would just make it clear that you’re not interested in paying for the flush & specifically want the 20 quart fluid exchange with the ATF machine (without the use of aftermarket flush or additives). The shop foreman and mechanics are trained on the issues with these transmissions and should closely follow the prescribed service procedures or service bulletins. The service writers on the other hand may not be aware & so when scheduling the work the request needs to made clear and documented in the write up. Furthermore, I had to request the Mobil 1 synthetic ATF HP fluid (blue label), as they don’t stock it.
This is my opinion.