Honda Accord LX check engine light, tranny, & code

So I bought my Accord of Craigslist from what I
thought to be a trustworthy guy ( yes I know, my
mistake ‍♀️) long story short he had someone turn
the check engine light off and now I’m stuck with it,
but I’m not too mad bc it’s a solid car regardless of
the issues I am having, it’s got a lil over 240,000
miles on it  but he’s a fuckin beast
Anyway this fuckin code P1457 EVAP control
system leakage (evap canister area) is coming up
I have recently changed the oil and put in some
Lucas oil treatment to stop leaks hoping that if
there were that would fix any leaks but so far no
luck.
Also the mechanic that I have working on the car
wants to change the tranny fluid because I have
told him The Pickle (which is my cars name) shifts
funny it’s almost like a hiccup. But I’m hesitate to
have him do it because I’ve heard mixed opinions
on whether or not to change/flush the fluid because
it’ll cause more damage then it’s worth.
I just need to get my Pickle inspected so I’m not
driving around just waiting to get a ticket. Someone
please tell me something