No probably not. I'd specialize in one and then maybe as a subfield or long-term project you can still keep the other in mind.
If you do modern India you'll be encouraged to think comparatively within South Asia especially doing readings about Pakistan,Nepal, Bangladesh, as well as getting to grips with the tremendous internal variation of India. I can't speak for Iran but I imagine your encouraged to look for your comparisons to other arabic countries - unless you have some compelling case for the comparison with India above being interested in both.
Also what's great about doing Modern India (probably also true for Iran) is that there are a few parallel disciplines to history which take up the topic. You might want to keep in mind disciplines like international development, South Asian Studies, or political science in order to broaden your search - there could be excellent supervisors or more funding opportunities outside history.