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Modifying a bare repo directly

Hi -

Is it possible to modify a bare repo directly? e.g. is it possible to
insert a file into a bare repo without first cloning a non-bare copy?
I'm thinking along the lines of a command or sequence of commands that
modifies the file index and then copies the file blob into /objects,
but in a situation where the new file exists separately from the
target repo.

Thanks -