You could paste this into a Kyma Notebook:
'037_2c#_99_testBasePitch.aif' fileNamesOfSameTypeInSameFolder do: [ :fN | fN asSamplesFile uiBasePitch: 0 nn; updateHeader].
Replace the file name with one of the files in the folder you'd like to modify, and replace 0 nn with the desired base pitch. Then select the entire line and evaluate it using Ctrl+Y (Or Edit menu > Evaluate).
Take care that the file name is unique (otherwise Kyma might find a different folder containing a file of that same name). You can do a group rename in the Finder by selecting all the file and doing a right click (ctrl+click) and selecting Rename... from the menu.