This is a little bit strange question to me. A lot depends on the detailed values of equilibrium constants.
Lowering pH you will protonate benzoate, so according to the LeChaterlier's principle solubility should go up. I am not sure though what is the concentration of benzoic acid that you will get - will it be high enough to precipitate benzoic acid?
Adding NaOH you will precipitate Ag+, effectively removing it from the solution. That means - again - that more benzoate will dissolve. However, I am not sure if solution containing sodium benzoate and precipitated AgOH (or perhaps even Ag2O from AgOH decomposition) can be still called solution of silver benzoate.
Could be solubility of silver benzoate is so low there is no risk of precipitation of neither benzoic acid nor silver hydroxide, I just don't know.
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