Currently re-installing Addons is not supported, because there is no way to tell Forge to stop using the existing deployed files without giving it time to detect the change and re-deploy the addon.

In order to implement this, the Forge registry file probably needs to use some kind of marker files.

.dodeploy
.deployed
.undeployed

So that it knows how to respond when changes are made faster than timestamps can detect. This would (hopefully) also in theory be a step toward multi JVM (multiple running forge / concurrent modification instance) support.

This has been partially implemented, but only naively. The files are actually re-written on UNIX based OS's, and will be re-loaded next time the addon is disabled/re-enabled, but this will not work on Windows.