Yes you can but not for your current company. You'll have to create a 'company scenario' and create a new company.

Notice: the 50x modifier was carefully designed to give you a fair game
and a nice career. Of course you have x50 fee but also x50 income.
Setting it to a lower number would imply that it may take you forever to buy
bigger aircraft.

The income modifier setting as well as several advanced settings is not available
in the normal create company dialog. This is why you have to create a scenario for that.

Open the FsPassengers folder and look into 'config/MissionGamesCfg/ a 'readme.txt' is
in this folder to help you create a new scenario.
Once done, create a new company using your scenario. Notice you can transfer
your pilot to this new company, they will play under the new rules.

See also:
How to find/open the FsPassengers folder
Can I modify my company setting after creation?
I want to edit the war zone because I don't want to be under fire at...
How to Create a Company with Advanced settings