Is there a rule that will prevent replacing a ball of a different type (eg 3 piece to 2 piece, hard to soft) during a round between holes? If so which rule is it?. thx in advance.

Look in appendix 1 ..part C

There is nothing stopping you under the rules …....except in the rare case thats its been made a condition of the competition

That’s good to know

The relevant Rule in the book is:

1-1 General
“The Game of Golf consists of playing a ball with a club from the teeing ground into the hole by a stroke or successive strokes in accordance with the Rules.”

That means that you must play the same ball from the tee to the hole, unless another Rule over-rides e.g. your ball is lost, unfit for play etc. However, it also means you can change your ball after each hole if you wish.

The only restriction would be where a one ball condition is in force under the Conditions of Competition for the event. This is normally restricted to “expert” players, but it would limit you to playing the same brand and model of ball for the duration of the stipulated round.

Thx everyone for the responses. I have always played the same ball type during a round. Now I guess I don’t really have to :)

The pros have to use the same type of ball for the entire round.
I think there was a story about Tiger in one of his Major victories realising that the ball he had in play was the only one he had left which could have put him in a very awkward position.
They can’t, say, change from a Pro V1 to a Pro V1x during a round. But that’s a PGA tour rule only.

It’s not a PGA-tour Condition only, it’s in effect for all professional tours.

But it may be used in any competition if for some odd reason the Committee want to.