Welcome to the forum! You'll get a variety of opinion on delete and tune for sure but I would lean towards the opinion of a truck that is deleted and tuned is a bit more reliable then not.
Likely not, for one, because a tuner typically will not edit another tuners file (at least one with morals) to do the delete. And funny enough, most of the "tuners" out there simply aren't qualified or know even how to do that outside of a "base tune" file.
Wish I had an active subscription, I would help you out. Otherwise, you can sign up for a 1 month subscription here for just $20 and get all the diagrams/instructions you need.
https://www.alldata.com/diy-us/
I would figure out a way to check the sensor, or the reductant level sensor may be malfunctioning or damaged, causing the P203E code to be triggered. Inspect the sensor and wiring for any signs of damage or wear.