Top 10 Golf Rules Myths
Whatever brand and type of ball you use to begin your round, you
must use that same brand and type of ball for the entire round.
We watch too much golf on TV and think we therefore
understand the Rules. The only time this myth is a fact is when the
‘one ball rule’ is in effect. That is generally only a condition during
PGA Tour and other events for highly skilled golfers. It is almost
never in effect for regular play.
To answer the OP:
During the play of a hole, Rule 15-2 says that the player may only
substitute a ball if he’s proceeding under a Rule which permits him to
play, drop or place a ball. In general, then, you can’t substitute a
ball on the green unless the ball is unfit for play.
Rule 5-3 says that you can
substitute a ball for a
ball that’s become unfit for play as defined in that rule. So if the
ball is cracked, out of round or cut it may be taken out of play and a
different ball substituted. (Scrapes alone however, such as from
hitting a cart path, don’t make a ball unfit for play.) There’s a
procedure in 5-3 that tells you how to go about informing your opponent
or fellow competitor before you make the substitution.
There is no restriction on substituting a ball between play of
holes, so putting a different ball in play on the next tee is perfectly
fine. Check your local rules or conditions of the competition to make
sure that the mis-named ‘one ball rule’ isn’t in effect, though. That
might limit you to only using one brand and model ball during a given
round. It’s rare to have that rule in effect for casual rounds.