I'm seeking assistance in configuring a message handler client event script across all projects in Ignition. Currently, I am utilizing the system.util.sendRequest function to send messages from one project to all projects on the same gateway. Is there any way to share a client event script across all projects?
Not really, no.
Client event script are an inheritable resource, but on an all-or-nothing basis. So while you could put such a message handler in a globally inherited client event script, as soon as anyone edits a project's client events by overriding the resource, that script will be "frozen" at that version from then on.
The closest you can get would be to put the functionality in a globally inherited project script, then make all the projects have a one-liner in the message handler setup that just delegates to the inherited project script. (Event scripts should always be one-liners pointing at library script functions, IMNSHO.)