I do know 2 guys that put spaces behind their grips in order to change the effective draw length on the bow. ALthough the powr stroke and actual draw length did not change, by moving the grop back it effectively changes how far they actually drew the bow. It did not increase the speed in any way, but it did get noticeably louder.

For a point of reference, here is the table for shortening/lengthening cables and strings:

Sting and Cable shortening Table

On a 2-cam bow:
Shorten string, leave cables the same = shorter draw, lower weight, little change in BH
Lengthen cables, leave string the same = shorter draw, lower weight, slightly lower BH
Shorten cables, leave string the same = longer draw, higher weight, slightly higher BH
Lengthen string, leave cables the same = longer draw, higher weight, little change in BH
Shorten string and cables by the same amount = same draw length, higher BH and higher weight
Lengthen string and cables by the same amount = same draw length, lower BH and lower weight.

On a 1-cam bow
All the same, except for last 2 - to keep same draw length, you need to shorten/lengthen the string by 2X as much as you do on the cable (because the string goes between the ends of the bow twice, not once).

The actual amount of change varies depending on the bow and the amount of cable/string change.

A slight addition -- if you shorten both strings and cables(cams now clocked same as before, only you have a higher brace), you get the same power-stroke, but the actual draw wlngth will be longer by nearly the amount you increased the brace.