It's only something you can do in the Advance Rules:
Add a set of nation rules for England and choose to add extra league and cup to the existing structure.
Choose 'Convert to Advance Rules' in the 'Rules' menu
Find the league you want to edit in the left hand menu and expand it.
Click 'Competition' and scroll down until you see 'Fixture Rules index', remember the number in the box.
Go back to the left menu and expand the nation (England in this case)
Expand 'Fixture Rules' and then click on the number you remembered 2 steps ago.
At the bottom on this page are the squad selection rules, add a new 'Annual Wage' rule with your require cap.
Save, Test Rules>All, then run it in FM14