I have an extrusion from a primitive which is attached to another face. What I want is when the size of the main object changes there will be less extrusions. This image should help understand;



When the shape is larger there are less spikes, when it is smaller there are more spikes, but I want when the shape is larger to control not only the amount, in this case of subdivisions of the outside shape, in this example the circle; but also delete excess spikes and move and merge the points of any remaining spikes to the nearest subdivision on the circle in this example, I hope this is understood ?

I'd approach it this way -
drive the divisions of your circle by it's radius - small = more divisions, large = fewer
group the divisions and use that group in the extrude
the amount of extrusion can also be driven by the radius of the circle.

What about the merged parts sorta like spikes on a bicycle wheel, I assume the delete node can delete excess merged extrusions ?

if the extrudes are driven by the radius they should all come together to a point - then a fuse I guess, depending on what you want to do.

I ask because if I create 5 spokes, when the object gets larger I'll need 12 spokes how will it know where to place the spokes, especially if I want the spokes, lets say three primitives apart but as though they were merged and modeled seamlessly, then when the object gets smaller, those spokes are deleted, the last part the delete node probably will work, not quite sure ?

will the number of spokes be animated?
if not, the group SOP can group primitives on 2s or 3s etc, so you can have a spoke, then 3 prims, then another spoke etc.

get started on this and post your results and we can see where it needs some help.