Hi

My understanding (16-1c) is that old hole plugs or pitch marks can be repaired at any time - even if you aren't actually on the green.

Any other damage e.g. spikes marks cannot be repaired if it would help you in playing the hole - as a good citizen of course you are free to make repairs once you have holed out.

Generally speaking the line of the putt can't be touched or improved but pitch marks, plug holes and loose impediments are an exception to this rule (16-1a) - depending on who you are playing with it might be worth showing them what you are doing to avoid misunderstandings afterwards.

Hope that helps.

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I firmly believe that we should try to experience all that life affords, except, perhaps, bestiality and of course Morris Dancing.