How to manually set the head table values

Glyphs
1

I want to forcefully set the head table values. In the Custom Parameters section of the Masters tab, I can add other values (such as hheaAscender, TypoAscender, etc.), but I cannot find anything related to the head table. I want to set the values for head’s xMin, yMin, xMax, and yMax.

2

Why would you change the min/max values? They should match the shapes in the font.