In theory, yes. However, if Prince Charles can talk about global warming and his other political hobbyhorses, then other British royals expressing their views on immigration and Muslim enclaves in the UK wouldn't be any more out of line.
It’s a fine line. Royals are expected to have charities they sponsor. When I took a cruise on the QM2, there was a talk about the charities of the Royal Family, and there was a request to donate to Prince Charles’ charity.