OsX and Time management

Dear all!
I would like to develop a small app that does this trick:

for a certain user, or at best, certain application, fakes the system data.

I'm really at beginning so I don't understand if I can do a very trivial change
in the system time, pb terminal command , or I can do a
more sophisticated version that in function of which app is running, fakes only
for it system time.

Where I can find information to do it ?

Cheers !

Fake system data? or date? What is the end goal of this application?

I would like to tell myself which date its to an application

In theory I could tell to all the system which date it is by DATE command
but I would prefer to tell only to a specific application.

It could be any application, in the case it uses standard ways to
understand which is the date

My goal is to extend the time before an app expires after a fixed amount of time

But before this, i really don't understand how the date time information is obtained.

Hope not to have broken any forum rule, asking this thing.
In the case just edit my comment....

Yeah that's not legal and we're definitely not helping you with that. Developers spend their time and energy developing apps, if you are using a trial version and like it, pay for it. If not, seek out free alternatives, but don't cheat the developers!