Is there any way to change the season length?

I have a trainer to do that but it doesen't seem to work.

I don't want to play 89 games per season, i work and have a personal life, it would take me about 3 months to finish a season.

Can i change to 29 games or something?

You don't need a trainer. In both Association and Season modes you can change the season length before you start.

i forgot to say, im playing in my player mode.
you can't change it there!