what are my chances? brake cables

[Ajax Bay]

Since the OP's asking the question the implication he has not replaced the cables on this bike before. Am not suggesting that outers don't need replacing regularly. They don't (shouldn't) need replacing frequently, though. We don't know why OP has decided he needs to change the cable: perhaps the end has frayed after a cable end cover fell off and is looking untidy cf @Profpointy 's experience (and us all I suspect, occasionally).

I want to change my inner brake cables . . If I remove the inner, what are my chances of just sliding a new inner back through?

He asked whether he can do it by just pushing through. Let's not bring expense/affordability into it: the OP may be short of time and replacing the outers will take significantly more of that. He can judge from the advice above that most people advocate replacing the outer as well.

 

[e-rider]

the outer cable doesn't need changing - it's only a few months old
the reason I ask is that I just changed calipers, and the cables clamp in a slightly different place, hence why I want to just put new inners in. I will try and let you all know how I get on.

 

[Kestevan]

Some inners (Clarkes I Believe) come fitted with ends for both shimano and campagnolo, and you have to cut the unwanted end off. These can be a swine to feed through. Your better off with the single ended cables which resist unwinding much better.

If you do have to cut the inner first, then you can try sealing the end with a touch of solder, or superglue which will make it much easier to feed.

 

[e-rider]

removed old inner brake cables, and put new ones straight back in with no problems - the outer cable lined up perfectly under the bar tape