Dealership won't change my transmission filter?

2002 honda civic 126,000 miles that had remanufactured transmission at 91,000 miles 6 years ago. Now i've done a fluid exchange every 2 yrs since then but i was now going to do a flush for $150 but the dealer says they don't remove the filter because it's sealed. Is this bad to keep the tranny filter in there for 6 yrs already?
I want the remaned tranny to last at least 91k like the original.

As Dennis says, the filter is inside the transmission and is not a simple spin-off, spin-on affair like an engine oil filter. It can be cleaned, if you wish, but that entails draining the transmission, removing the pan, removing the filter and cleaning it, then reassembling the thing and refilling the fluid. It's the sort of thing that's usually only done when the transmission is being difficult and is stripped for inspection and repair.

Should never need the transmission fluid changing ever

They probably didn't tell you the filter is inside the transmission and the transmission itself would need to be removed first.

The filter may not be serviceable. Meaning one may to tear a part the transmission to get to it.