you can make more than 300 by using quests which add to you skills
for example, if you got 300 repair skill and complete the quest which add to you +10 to repair skill you'll be have 310 repair skill
it will displaying in stats as 300 but if you open the fixboy there you can see 310( i dunno any quest which can add skill at the moment )
and other way - using console commands, like ~param 0 paramID count( available from tester and higher access level )