Try this
(?<!\||^)\\"(?!\|)
Input
\"DB\"|\"FB_\"ID\"|\"INV_\"ID\"|\"%T001\"|\"%T0\"16\"|\"OWNER_KEY\"|\"VEND_LABL\"|\"INV_KEY\"|\"FB_KEY\"|\"FB_AP\"P_AMT\"|...
Output:
\"DB\"|\"FB_ID\"|\"INV_ID\"|\"%T001\"|\"%T016\"|\"OWNER_KEY\"|\"VEND_LABL\"|\"INV_KEY\"|\"FB_KEY\"|\"FB_APP_AMT\"|...
solved How to remove quotes in between quotes using Regex? [closed]