More changes put around by ruler (7)
I believe the answer is:
Here is my best explanation:
'ruler' is the definition.
(emperor is a kind of ruler)
'more changes put around by' is the subsidiary indication.
'changes' is an anagram indicator.
'put around' indicates putting letters inside.
'by' becomes 'per'.
'more' anagrammed gives 'emor'.
'emor' placed around 'per' is 'emperor'.
(Other definitions for emperor that I've seen before include "Largest type of penguin", "Richly-coloured butterfly", "Beethoven piano concerto, Op. 73", "Purple --; -- penguin", "Character in 24 ac", "A moth; a penguin", "Napoleon Bonaparte, for instance", "Large richly coloured butterfly", "Type of penguin" and "Penguin of largest known species - a great ruler".)