In base, all I changed is on old Spanish queen (8)
I believe the answer is:
isabella
'spanish queen' is the definition.
(I've seen this before)
'in base all i changed is' is the wordplay.
'in' indicates putting letters inside.
'base' is an anagram indicator (base can mean impure or corrupt).
'changed' becomes 'sa' (I can't justify this - if you can you should give a lot more credence to this answer).
'is' becomes 'be'.
'all' with letters rearranged gives 'lla'.
'i'+'sa'+'be'='isabe'
'lla' enclosing 'isabe' is 'ISABELLA'.
'on old' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for isabella that I've seen before include "A queen of Spain" , "drab colour" , "Spanish queen who was patron of Christopher Columbus" , "Ferdinand V's queen" , "Consort of Edward II" .)