It just might be that the renowned researcher and historian is confused.
According to Wikipedia, there is a second Taj Mahal that was renamed from Raj Mahal at the suggestion of the British Resident at Bhopal.
That doesn't prove anything—it might even point to a British habit of suggesting other names for things that already have a name—, but still...
However, here we find
The Taj Mahal, one of the seven wonders of the world, is a symbol of love. It is greatly admired as one of the most magnificent monument ever created by an individual in memory of his beloved. The Taj Mahal was built by Shah Jahan in memory of his beautiful queen, Mumtaz Mahal.
A township was built for the workers near the monument and named Mumtazabad. The actual name of the Taj Mahal was Ruazaye-Mumtaz Mahal during the 17th century. However the British, during the 19th century, renamed this monument and called it the Taj Mahal, because Mumtaz Mahal's alias name was Taj Bibi.
So, this seems to corroborate the renaming of the famous Taj Mahal, but it also claims that the English renaming stuck (contrary to the claim). Also the name "Ruazaye-Mumtaz Mahal" isn't to be found anywhere else on the internet. :(
And there also this, which might be related:
This P. N. Oak we also find in a comment on History SE. Is he/she supposed to be (or represent) '[t]he British' from the claim? He's not British (and also, less relevant, characterised, by some, as a "crackpot"). Someone familiar with the context might explain whether this is possibly what the claim is referring to.
