How can I do that without messing up the footprint?

If you have the Library Expert Enterprise, you can globally change the solder joint goals open Preferences and Save File as Hand Solder to create a new Preference file.  Then select > Terminals > Terminal Type > Density Level > Toe > Heel > Side

Or if you are using the Library Exert Pro you can change the Solder Joint Goals locally by selecting the Terminal tab and then the Density Level tab and edit the Toe, Heel and Side. 

Note: you will always visually see where the terminal lead is on the pad stack. Most Hand Solder projects require a larger Toe and possibly a slightly larger Side, but the Heel value is not necessary to change unless it's a gull wing terminal lead. But even then, the heel value is already robust for hand soldering.