It means you cannot use your 'power' to set another precept or raise another type of tax.
If your spending requires the (normal) precept to be raised, then it can be done but it has to be done at the proper budget meeting.
What this paragraph is trying to prevent is stop a parish creating a 'village green precept' or any other type of tax (applicable to all).
The reason is that a parish can charge (e.g. charging for a car park, or for stalls at a market, so it tries to ensure that there is clear difference between the Parish creating charges (for services), than creating an additional precept other than that 'official' precept.
To be clear, you can raise the precept to cover ANY legal spending, but you not create a new type of tax. You can create charges (that only apply to the user, e.g. village hall bookings).