See, there are no clear rules on this. When you enter the country on the visa, it goes in their system. When you exit the country on OCI, it will flag somewhere. Knowing our motherland, the person you are dealing with may let you get out without any issue or may create trouble depending on how his/her mood is on that day.Entering India with visa and exiting with OCI shouldn't be an issue AFAIK. They will check the passport for the visa and if they see the visa, they won't ask anything further. You can show your OCI if you are asked.
A small story: one of my older relative is Australian citizen but has Indian heritage. 10+ years go, his OCI card expired and he didn't know he had to change the particulars/get new OCI. He came to India and was given a very rough time at the airport. Exact words of customs officer, "You are a foreigner now and your country gives grief to Indians when they go to your country and we'll reciprocate". Poor guy had to sit at the airport for 6+ hours and then run around 3 days in Delhi to get it sorted out. So, be prepared!
My two cents: if you enter the country on visa and you stay goes past 6+ months, get your visa extended through FRRO. That's an online process and you may have to pay some fee but you'll get the piece of mind. You may want to check with FRRO when you are in India if changing status from visa to OCI is okay. Good luck in either case!
We are also going through the same BS right now so your experience will be very valuable