Hi, you can try push processing. Usually high speed film. Underexpose the film and overdevelop the film. For example, expose Ilford HP5 (iso 400) at ISO 3200 and push process (overdevelop) by 3 stops. For color film good results can be obtained with Fuji 1600. You have to push process color film using a Dip and Dunk film processor. Regular roller transport can not due to it's fixed developer, bleach and fixer time/temp.
Ok, I was not telling you the truth. It is possible to push process color film using a regular roller transport if the lab operator is willing to do so. Make sure there are no other rolls in the machine. As soon as the film cuts from the cannister (you will hear a loud selenoid actv. sound) wait 2-3 sec. to allow the end to fully immerse. Turn off the main drive. Try, lets say 20 seconds, then turn the drive back on. Bleach and fixer time will be normal. For testing purposes , ask for snip test (lab will cut only few frames for testing).
With color film you can not push too much, it will look flat if you over do it. For B&W you can go to extremes but contrast will be very harsh.
Have fun
