The O'Kelly, as in the first posted game can easily transposes into a Nadjorf
if White goes for d4. (more about transpositions later...I can knock that c5 pawn back to c6!)
3.c4 stopping b5 and d5 is a playable, White has holes on d3 d4 so throw in
a d4 and get a bind up - though you may meet players who like playing
against it and know a wee bit more than you.
(if they are common O'Kelly players then there is a strong chance they will.)
But as long as you don't faff about and neglect opening priciples then you
should be able to play any opening. The rule being if in doubt get a piece out.
At this level bring out your bits, grab a fair share of the centre and castle.
Only look for opening kills if you are sure they have broken an opening rule.
Then you must jump on it and react.
A bad opening move can easily turn into a thorn in your side if it is not punished.
If you are gambit inclined toss in 3.b4. and then a3.
or 3.a4 if you want to annoy them.
The plan here is pretend you are Black facing an English (1.c4) and take it from there.
Always be on the look out for transpositions to another opening.
The O'Kelly can swing into a Caro Kann if White playes 3.c3.
How can that happen. A Sicilian is 1...c5, A Caro Kann is 1...c6.
And now from the Caro Kann