Cycles Convolution Matrix (Kernel) According to this post:
voronoi cracks fac

Is it possible to refactor the texture and use it from outside the node group?
So it would be possible to have an Convolution Matrix Node.

P.S. Why are the 2 nodes muted?:
The 1st set of nodes (add and subtract nodes) are used  for offset the coordinate .. it is 3*3 convolution filter ..so it can use 9 voronoi/image texture ..so if you adds 0.5 in one of the add node , 1 texture will offset  0.5 unit scale..
If you add/subtract 0 in those node that means that node will not offset .there are 2 add node because 1 is x axis and other one is y axis.
So if you mute those 2 add node it doesn't matter cuz it is not offseting anyway...soorry for my bad English