Is it ok to switch from amlodipine 10 mg to perindopril 4 mg in known hypertensives? the switch is due to development of ankle edema

Yes: Ankle edema is a side effect of amlodipine. Peridnopril is an acei inhibitor which typically does not have such side effect.

It is ok: Perindopril is ace inhibitor and amlodipine is calcium channel blocker, typically in my experience, if you required 10 mg of amlodipine to control bp, perindopril 4 mg may not be able to control bp. Some times, if we cut amlodipine down to 5 mg and add acei, works well and edema might resolve( chance of edema is lot higher with 10 mg compared to lower doses).