This is incorrect. Reagan's Eleventh Commandment was "Thou shalt not speak ill of another Republican".
His goal was to keep deadly infighting to a minimum in primaries to allow Republicans to pull together to capture political offices in the general elections.
On the surface, it appears to be an idealistic goal. But it was a canny one. Reagan himself was a master infighter and great strategist in political campaigns. But his commandment was not just a statement off the top of his head. He knew what he was saying. He was cautioning against EXCESSIVE PUBLIC smears among rival Republican candidates in primaries. It only weakens and discredits the party and makes it more difficult for primary victors to take on the Democrat candidates.
His words are just as true today as they were at the time he uttered them.
Leni