Changing the seat might be a possibility but probably a slim possibility because if you wanted to go with a mesh seat, you would need a frame that attaches to the trike to accommodate the mesh. It wouldn't be cheap, probably too expensive to justify for a $500 trike.
I'm sure somebody here will pipe in to say they love their hardshell seat. They are common on some of the faster two-wheeled recumbents.
Next Monday June 5 is the anniversary of my arrival to Las Vegas from Findlay, OH. That was 1985 and it was 105 degrees when I arrived after interviewing for a job here in the Spring when it was a beautiful 80 degrees. I thought I might have landed in Hell when I came out of Utah and it became increasingly hotter the closer I got. You do get used to it.