jordan mccoy

i bought a 98 subaru impreza rs with a 2002 wrx swap off of ebay. it came with the pclink already installed so i am new to it. it wasnt his daily driver so he had it tuned for most power, so it get about 10 mpg. im 16 and cant really afford that, so i was goin to change the air/fuel ratio to get more mpg's and change it back when i wanted to have some fun. is all i have to do is change the master and lower my boost.. have the equation i was just wondering if that is all that i would have to do and cah switching the settings back and forth damage anything