$unlockdefinebones

$unlockdefinebones is a QC command available in all Source games. Normally, the $definebone definitions are always used for the default positions and rotations of the skeleton. Setting $unlockdefinebones will instead use the bone positions of the first frame in the last defined smd/dmx file of the qc for the definebone values.
$Unlockdefinebones will not shuffle the order of the $definebone lines, unlike the studiomdl command -definebones would.

Tip:If you define your $model, $body, or $bodygroup at the very end of the qc, or at least below the $animation and $sequence, you will generate new definebones based on your new ref pose without shuffling the definebone order.
This would be very useful for viewmodels that have arms and weapon separated, where a different definebone order causes issues. Such as in Left 4 Dead 2

Note:This behavior is the opposite of the default behavior in previous versions of the model compiler. For Half-Life 2: Episode Two, the default behavior was changed to stop the more common undesirable effect of animation order messing up default locations of bones - such as those used by attachments - that were only actually defined in a small subset of the source files. The drawback is that some badly exported LOD models - ones whose skeletons don't match their actual pose since they're no longer attached - now will show the previously hidden errors. Setting $unlockdefinebones will get the old behavior back.

Syntax

$unlockdefinebones