I don't know what you mean by safe, but killing a crashed app will not hurt anything. Are you having that many problems with apps crashing? Or is this just one app in particular?
Read the manpage for lpc.
lpc kill all
lpc kill printername
will kill lpd then restart it. It won't kill the jobs in the print quere. Might also want to look at: redo
Are you using the driver that came with your distribution or using one from Lexmark?