Each Feature has a method called SetEndOfPart which takes boolean as argument. If you want to "Edit" a particular feature, first you need to call SetEndOfPart(true). This moves the "Part End Marker" to above this feature. After this do the necessary changes in the feature you were looking for. After this do not forget to move the "Part End Marker" to the end of this feature by calling SetEndOfPart (False).
The code below changes the workplane of a hole feature in the attached part.
Public Sub ChangeOfFace()
Dim oDef As PartComponentDefinition
oDef = m_inventorApplication.ActiveDocument.ComponentDefinition
'Get the hole feature
Dim oHoleFeat As HoleFeature
oHoleFeat = oDef.Features.HoleFeatures.Item(1)
'Move the EndofPart position before Hole feature
Dim oWorkplane As WorkPlane
'Change the workplane
oWorkplane = oDef.WorkPlanes.Item(5)
'?Set it to hole feature
'Move Back the EndofPart position after last feature