I need to slowly migrate a legacy codebase to a new design.

The old design uses the default $spacings provided by Bootstrap 5. The new design has different/additional $spacings:

$spacers: (
    0: 0,                   //0
    1: ($spacer * .25),     //4px
    2: ($spacer * .5),      //8px
    3: ($spacer * 0.75),    //12px
    4: ($spacer * 1),       //16px
    5: ($spacer * 1.25),    //20px
    6: ($spacer * 1.75),    //28px
    7: ($spacer * 2.5),     //40px
    8: ($spacer * 3.75),    //60px
    9: ($spacer * 6.25)     //100px
  );

How can I conditionally set the $spacings?

Ideally something like this: if the code is inside the CSS class .new-spacings then use the new spacings, otherwise stick to the old ones.