Allocating rural exception sites - Public forum - Planning Advisory Service (PAS)

(I posted this earlier today in the General discussion forum, but it is really a plan making query, so am now re-posting it here.) Does anyone know if you can allocate rural exception sites in a local plan, as opposed to having a policy that allows for them to be granted permission if a need is demonstrated? The now deleted PPS3 said that LPAs should consider allocating and releasing sites solely for affordable housing (AH) using a rural exception sites policy, which enables small sites to be used for this use in small rural communities that would not normally be allowed. However, the NPPF merely says that LPAs should consider planning for housing development to meet local needs, including through rural exception sites where appropriate. The glossary defines these as small sites used for AH in perpetuity where sites would not normally be used. My understanding is that rural exception sites are not normally allocated in a plan, as they are usually brought forward by the local community after a call for sites and a local needs survey. Also, allocating them in a plan would presumably affect the land value and make AH unviable (unless specifically allocated for AH). However, I cannot see anything to stop us allocating a rural exception site. As a follow up question, assuming we can allocate a rural exception site, would this also apply in a Green Belt area? The NPPF says that "limited affordable housing for local community needs" is not inappropriate development but would a Green Belt review be needed in order to allocate a rural exception site in a local plan? Thanks for your help.