Yes, you can use the 'hilite_system' function.
If you want to highlight only pieces of the model you selected you would first need to find the handles for each block and line. This can be done by using 'find_system'.
Example code for highlighting a group of blocks and lines you've selected:
selectedBlocks = find_system(gcs, 'SearchDepth', 1, 'FindAll', 'on', 'Selected', 'on');