how can i bypass an input or output from a udf?

function[m2,P2P1,T2T1,Po2Po1]=oswbudf(m1,y,b1,cp,r)

in this udf sometimes i dont need the third and fourth output i just need the first two. so is there a way i can bypass these and just get the first two outputs?

also function[m2,P2P1,T2T1,Po2Po1]=oswbudf(m1,y,b1,t1,cp,r)

i need a way in which i give only one of the two inputs (from b1 or t1) and depending on the input that was given the udf executes different lines of code for each case. is this possible or should i write a separate udf file for that?