A split shift by definition is working X hours of your 8 hour shift, taking a length of time off in between, then working the remainder of your 8 hour shift later in the day.
Ex. 6am-10am, off 10am-2pm, work 2pm-6pm
If you're an FLM, the ATM can assign you anything, including split shifts.
If you're a CPC, you are protected by the contract and your Basic Watch Schedule MOU.
You can, however, request a split shift for an unusual circumstance. It requires approval, but it can be allowed.
Ex. You're taking a FAM trip in one day to go tour a facility and check out the area. You're "working" on your first flight there and during your tour, say 8am-1pm, then "working" on your return flight home, say 7pm-10pm.
If you're talking about mids, the directive that just came out was mainly directed at the facilities who abused the system (first person works 4 hours, then goes home for the final 4 hours while his buddy signs him out or the reverse, Person A works the first half, Person B doesn't show up until the final 4 hours but was signed in at the start of his shift).