No.
Alright, so here we go:
You can't set a specific map. Team9000 Launch is not a hosting service - the servers it launches are not set up in your name and you can't control them like you could if you rented one from a real gameserver provider (for example, nfoservers.com). These servers from Launch are free and are designed to facilitate a short time of mucking about with other members of T9k. Now, I don't actually play GMod, so I'm not sure how the map is selected, but I would imagine it's either randomly selected from a preset list or there is only one map option. You have nothing to lose by setting it up to test it out, it's free. You don't have to worry about causing problems by launching it either; all servers automatically shut themselves down after a period of inactivity (nobody logs in and nobody is on the server). I believe it's 60 minutes, but I'm not positive.
Basically this, and I'll add a bit more.
The map list is in a set rotation. This is mainly due to Gmod being a game that is designed to be modded, and as such, people are going to want more and more. The more we add, the more resources the server takes. So, most game modes will run the stock map list to avoid issues.
If you'd like more maps to be added, find a link to a download of said maps, go
here, and explain why they should be added IN DETAIL. "Because it's better." "Because it needs more maps." and the like are not valid reasons to put work into the way servers are set-up.
If you do the above, do not expect immediate action or an immediate response. Launch and everything involving it is a personal fun project for Wooty for the members of Team9000. He has other things that he wants to work on and will get around to it when he gets to it.
Launch servers, if empty, will close down in 60 minutes, meaning they aren't permanent by any means.