There is quite a difference between old and new spacing rules. I fear that we will have some very inconsistent layout if we mix these values.
An option could be to ask the designer to map the old values to the new ones.
$newSizes: (
5: 5px
);
$s1: map_get($newSizes, 5);
Also notice that the new values are using pixels units and no longer REM - how should we approach this?
This issue also goes for typography, and to some extend colors.