My understanding was that it is the club that is declared champion that gets into the playoffs:
https://spfl.co.uk/pages/rules-and-regulations
“SLFL Champion” means the club playing in the SLFL in any Season (excluding any
‘Guest’, ‘colt’, ‘B’ ‘second’, ‘reserve’ or like or equivalent team which is part of a Club
participating in the same Season in the SPFL and which shall not, under any
circumstances, be considered to be eligible to receive the title of SLFL Champion or
any other title related to its position in said league, or qualify for or be eligible for
participation in the Pyramid Play-Off Competition at the end of any such Season)
which is declared the Champion club of the SLFL based on the criteria specified in the
rules of the SLFL;