'[^']+'         # NOt a single quote between 2 single quote (i.e. strings we don't want to convert)
(*SKIP)         # skip this string
(*FAIL)         # fail to match
|               # OR
w+             # 1 or more word character

L$0        # lowercase the whole match (i.e. the string NOT between quotes)

case
when table.attribute = 'CaseSensitiveStringValue'
  then 'OutcomeValue'
  else 'OTHERValue'
end as casename