Its a little hard to understand your question, if you want to try out other mods, simply copy your original Freelancer directory and install the mod into that folder. Have multiple copies for a different mod each.
Discovery freelancer works fine in Single-player mode, there is no story though.
What I ment is that previous discovery mods have had it where you can give yourself like millions of credits to try out ships and what not in open single-player
You can do a lot of testing in single-player. Use 'help' to get a list of commands. Basically a command with no arguments will display a value, give it some arguments and it will try to change the value.
cash <nnnnnnn> will show or set your cash
system nnnnn will show or set your system etc