Most likely, that will do what you want, but it also depends on how many amps (A) the system draws right now, and how many amps the new battery is safely capable of putting out.
Realistically you are probably only getting half the Ah from the SLA that they are rated for, so an even smaller battery might work than 30Ah. Personally I'm all for as many Ah as I can get on the bike, because I never know if it will be windy or not, or if I have to detour around things by miles to get where I am going, on long trips.
Keep in mind that fully charged your SLA are closer to 27V than 24V. You should check to see what the fully charged voltage of your 24V LiFePO4 pack would be--if it is an 8s pack, my guess is about the same voltage as the SLA or a bit higher, depending on quality of cells and amp load pulled by system.