The ability to adjust your feedrates along your toolpath is included in GibbsCAM version 6.0 and later. To use this functionality right-click on the operation and select Utility Markers. U markers will appear at every position where a feedrate change is occurring. To add changes drag the U from the Utility Marker dialog and place it on the red toolpath lines.

You can also use the 'Change Feeds and Speeds' plug-in found under Plug-Ins-->HSM to apply changes to the feeds and speeds of an operation