The poem gives instructions on how to solve the puzzle. Each line has one letter changed, you need to look at these new letters and disregard the original ones (which spell BAD SET OF LETTERS TO BE FINDING). This gives a line similar to one from Simon Sends: MBKCYCKCRGKBMCGCRCKCRKKCWC = R - 5 (E), G - 4 (D), B - 2 (B).
You’ve discovered my puzzle that’s Mased on a game!
PleBse don’t blow it up. It’d be quite a shame.
But you’ll have a gluM IKEOlogy unless
I give you some clueC that you can address.
The first stYp you’ll probably find not intense.
Does a module make Chis sequence make sense?
This is seeming sK wRY! O ME, O my!
You should stay with the poem to keep Ceeling fly.
The theME I KEep finding as likeRy apparent;
Be aware whGre things are and the rest is transparent.
A leKter like this we find often exciting,
but its home is the feaBure you should be highlighting.
You’re making good progrMss! Don’t let yourself fall!
What you have Cight now is not quite yet all.
The long yarn-like Gubstance from a programmer’s hives
ExisC with restrictions of a six and two fives.
What you’ve cRvered already? That’s just the start!
Keep Carreling forward and you’ve got the part!
In your restrictions you havK two of the same.
IC they didn’t start similarly, that would be lame.
Hopefully now you should have your faRr share
of some interesting thiKgs; from each, take a pair.
The rest may be obvious, but to cross that borKer,
put the remainder in alphabetCcal order.
If it doesW’t make sense now, you might just be sickly.
The puzzle based on a Came has now been solved quickly.
After following Simon Sends rules, we get 3 positions in the poem. Next we must add the next 4 more characters to two of these positions and 5 more to the third (explained in stanza 8). These give 3 NATO characters with one additional letter, creating 3 pairs of letters. Looking at the pairs in alphabetical order (stanza 12) provides the answer.