On April 9th The R&A and USGA have published two new “Clarifications” (read about what a Clarification is on this link), one of these giving Club Committees an option to put a new Local Rule in operation.
In short: Under the new 2019-Rules of Golf (Rule 4.1b(3)) as a starting point you are not allowed to replace a club during the round, although it is broken/damaged (not if it is yourself that caused it to be broken/damaged). This probably so that players are not spending too much time on running back and forth.
But as of April 9th 2019 the Club Committees can put a Local Rule in operation, where it is allowed for a player to replace a club during the round if it is “broken or significantly damaged” by the player/caddie, which means that:
- the shaft breaks into pieces, splinters or is bent (but not when the shaft is only dented),
- the club face impact area is visibly deformed (but not when the club face is only scratched),
- the clubhead is visibly and significantly deformed,
- the clubhead is detached or loose from the shaft, or
- the grip is loose.
A club face or clubhead is not “broken or significantly damaged” solely because it is cracked.
You cannot replace it in cases of “abuse”. It is not clarified what “abuse” is. Maybe it means that a player cannot intentionally damage a club for the purpose af then being allowed to replace it with another club (that he/she would rather prefer).
The other new Clarification simply states that when taking relief under the penalty area Rules’ “Back-on-the-line-relief-option”, the reference point must be outside the penalty area.
You can read all the Clarifications (including the wording of the new available Local Rule) on this link (USGA’s website).