I beleive that the 50% rule should only apply to a player that does not already have a full bet (exact change) in the pot, regardless of limit/no limit. In the case of making change, that is not allowable, players can not just reach into a pot and make change at will, that is the dealers job and the dealers job to inform this rookie that he /she can not do this and if it happpens again that it is punishable by beheading.
Thanks for the education, really.
James