Facebook privacy

Hi.
On my facebook posts I use a custom privacy setting so the posts omit certain people within my friends list which works absolutely fine until the next time you make a post that deviates from the custom setting as it then makes all future posts default to last setting,say friends of friends for example.

This then means totally recreating the custom list,and for me considering I have over 100 people in the custom filter it takes considerable effort not only reworking the custom list but actually remembering who was in it.

Ive tried all sorts of workarounds but theres no simple answer unless anyone on here can point out one.

Thank you.