Changing markers on line

Have a lot of data, and when looking at full view I'd like no markers, but when zoom in to see individual points I'd like to place markers on the graph.
Planing on attaching some code to events to toggle markers on my line.
Is there a way to change the markers a line uses after it has been plotted, or do I have to clear the plot and replot?

Any suggestions appreciated
Thanks
Steve