Changing sides in allegiance — to them? (7)

I believe the answer is:

royalty

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'allegiance to them?' is the definition.
I can't tell whether this defines the answer.

'changing sides in' is the wordplay.
'changing' becomes 'royal' (I can't explain this - if you can you should give a lot more credence to this answer).
'sides' suggests removing the centre (I've seen 'sides of' mean this (only the letters on the sides remain)).
'in' becomes 'trendy' ('in' can mean trendy or fashionable).
'trendy' with its centre removed is 'ty'.
'royal'+'ty'='ROYALTY'

Can you help me to learn more?

(Other definitions for royalty that I've seen before include "Kings, queens and their offspring" , "Kings, queens, etc" , "Regal folk" , "Queens, emperors, etc" , "(Rank of) kings and queens" .)

I've seen this clue in The Times.

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