Exactly what mrbones said but also
when Pokemon moon and sun come out you will be able to transfer your Pokemon from
Yellow/Red/Blue to Moon/Sun
So its not a complete worry, your not wasting your time playing them..
as to answering your question though unless you bought a gameboy advanced colour and purchased a copy of yellow/red/blue and then used a cheat device then you cannot cheat.. however there are ways on youtube on how to glitch Pokemon like MEW into gen 1 games and then ready for gen futures..
goodlucky happy gaming, not sure if I helped but its a collection of opiniated views.