Can you really not get a computer? Most of the consoles we care about around here can be played on ancient PCs these days, never mind the still very useful £50 range refurb machines (less if you can refurb your own machine -- an old core2 era thing with a few gigs of RAM would be more than enough here).
IOS, and websites, do have some amount of general purpose tools (be it hex editors, tile editors or disassemblers/assemblers) that you could use to effect a hack worth playing, however if you are having to learn it and interpret it in such a way that you can do it on IOS too then you are making things far far far harder than they need to be, and nobody should approach ROM hacking expecting an easy time of things to begin with.
All the best tools, all the most useful approaches, all the future development that I can see will occur on PC (and probably Windows at that), and all the existing stuff will be built for PCs so porting it across (and despite being rough around the edges many of them are still the results of years of hard won knowledge) is similarly not going to be terribly easy.