Yes of-course it is possible, first you select the cluster by clicking on the geometry, you can use multiple choice option, than on the right mouse click you prescribe the property you want i.e. mechanical or hydro or what ever.
What I'm looking for is the ability to insert a large set of values (from an external file) that vary from cluster to cluster. I am curious to know if I can assign these field values to each cluster without having to individually assign them with the process you described above.
Importing data for each cluster without having to individually assign them can be easily performed using flac 2D or 3D but not with plaxis because this software is used as a black box.