And I think if the constant is a ratio, like the fine structure constant, https://en.wikipedia.org/wiki/Fine-structure_constant no change can be detected, even if there were a change because the ratio will stay the same. Likewise a constant like pi will stay the same because it is a ratio.
There are 26 fundamental constants, ie values that can not be determined from theory alone and need to be experimentally measured, which all other constants can be written in terms of. And it's not even a specific 26; 1/c is just as valid a constant as c, and you could rewrite any equation to use that instead of c.
For ratios, the constancy of the ratio is exactly what they seek to test.
And I think if the constant is a ratio, like the fine structure constant, https://en.wikipedia.org/wiki/Fine-structure_constant no change can be detected, even if there were a change because the ratio will stay the same. Likewise a constant like pi will stay the same because it is a ratio.