You can modify a a value in a field--which can be a global field so that you only have to modify this in one record to lock all records--and use setting in Manage Security to lock out all edits to the records in all the records in your table or tables.
See "Editing record access privileges" in FileMaker Help and check out this particular sub section: "Entering a formula for limiting access on a record-by-record basis" for a detailed description of how to set this up.
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