DS-1 Mod help: If I just change the the diode in D5 to....

[Unrespected]

If I just change the the diode in D5 to a 3mm led, how much different will it change the sound of the pedal. I cant get the caps until later on, so I cant do the full mod.

[Transmogrifox]

This will make a significant change.  It will sound more "grunty" instead of the normal DS-1 "fizzy".  

Another thing I like to do with these head-toe diode distortion devices is to replace the other diode with 2 series 1N4002 diodes (or any 400* series, 1N4007, 4006...), which seems to add some dimension of "creamy" -ness to it.  This way, the asymmetry of the clipping is very noticeable, but not quite as extreme.

An LED usually is "on" at about 1.5 - 2 Volts, whereas a 1N914, or 4148 is about .6 to .8 volts.  This leaves and approximate 3:1 ratio of the positive half-cycle to the negative half-cycle, which is very potent.

A 1N400* series diode is usually on the .5 to .6 volt "on" range, so two in series produces 1 to 1.2 volts.  This way you get one waveform polarity clipping at 1 volt and the other at, say, 1.8 volts or so.  

This is my preference, but the moral of the story is, do the LED mod and don't worry about the capacitor until you can get it.  You may even like it better without the cap, though it's probably more harsh without it.