mixing srd and chain examples

Could i replace polymer (bead-spring) with big particles in in.srd.mixture?

If you are asking can you use SRD solvent with a bead-spring
polymer, then I suppose, though I've never seen such
a model. You would need to insure that the bond springs
do not induce overlap between the monomers, since SRD
particles expect the big particles they solvate to be non-overlapping.