Popular Scottish county, according to Brummie, shows tendency to remain unchanged (7)
I believe the answer is:
inertia
'tendency to remain unchanged' is the definition.
(inertia can mean a tendency to stay the same)
'popular scottish county according to brummie' is the wordplay.
I cannot quite understand how this works, but
'popular' could be 'in' ('in' can mean trendy) and 'in' is located in the answer.
'brummie' could be 'i' (where the crossword setter is 'Brummie') and 'i' is found within the answer.
This explanation may well be incorrect...
'shows' acts as a link.
(Other definitions for inertia that I've seen before include "Slowness to act, lack of strength" , "Resistance to change" , "Sluggishness - sloth" , "Lack of inclination to move" , "I retain (anag) - the tendency to retain same speed and direction" .)