Awfully base breaking in to dishonestly alter lawyer's record (8)
I believe the answer is:
casebook
'lawyer's record' is the definition.
(record of legal cases)
'awfully base breaking in to dishonestly alter' is the wordplay.
'awfully' indicates anagramming the letters.
'breaking in' is an insertion indicator.
'to dishonestly alter' becomes 'cook' (as in cooking the books).
'base' with letters rearranged gives 'aseb'.
'aseb' placed inside 'cook' is 'CASEBOOK'.
(Other definitions for casebook that I've seen before include "Record of legal or medical instances" , "Where detailed written records are kept by, say, doctors" , "doctor fictitiously created for consultant" , "Record of work" , "Medical records" .)