No foreign user ever dares to make structural changes to jets produced elsewhere - except when deciding to produce locally a new aircraft based on an existing foreign model. The Swiss are no exception to the rule. But they can have sent their aircraft to McDonnell Douglas in the States for upgrading. F/A-18 indeed started as a 7,5G machine, but was later upgraded to 9G.
McDonnell Douglas proposed a series of optional upgrades in 1996. These included upgrading to 9 g from current 7.5 g manoeuvre limit; 2,271 litre (600 US gallon; 500 Imp gallon) external tanks (land-based operations only); F/A-18E fuel tanks of polyurethane, offering up to 160 kg (353 lb) additional internal capacity; six additional chaff/flare dispensers; and cockpit upgrades using some F/A-18E technology, such as LCD upfront display and colour tactical situation display.
The F/A-18EF has a limit of +10/-4 G.
All g limits have a 150% design factor
U.S. aircraft prior to the F-15 were generally limited to 7.33 G ("design load factor"), which is 2/3’s of 11 G ("ultimate load factor") which is the structural fatigue limit that was specified and tested for those aircraft. That means the structure was designed to fail at the most critical 11g condition, considering fuel load, weapon load, airspeed, and altitude.
After the F-15, U.S. aircraft were advertised as 9 G aircraft. This would mean a structural fatigue limit of 13.5 G.