There are a handful of things you might get done if you are used to pokemon but by and large pokemon is a different beast to almost any other game and those exceptions do not include clubhouse games/42 all time classics.
First things first I did start off a little list of all the card games I could find on the DS and roughly what went, you can see it
http://gbatemp.net/threads/card-games-on-the-ds-a-discussion-of-things.332152/
I just took a look at the 1.1 version 42 all time classics and it looks like it is going to be a nightmare hack- it sticks all the files save for the sound and download play in overlays which are little files loaded in at runtime, ostensibly they are actual code but here you will also find all the graphics and whatever else. Basically it is about as hard as it gets for DS hacking- I will run through it if you want but any other game, assuming it does not use this same technique (I have seen it a handful of times before), is probably going to be easier to hack.
That said you might be able to fumble your way into some basic stuff here; I doubt it will be compressed beyond the initial overlay compression and assuming the game does not have a graphics/tile map (50/50 as to whether it has one and it will trouble you here) and you are just painting over pixels rather than adding new options or changing text lengths then it is not so bad.