Philippe MARTY
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There were some instructions posted that should give you sufficient idea.
You will most likely have problems at upgrade time, so plan a strategy to downgrade php to standard before you do a general upgrade of your server, & then upgrade php again after any major server upgrade.
It's easy enough to do, but you may run into unforseeable problems with dependency issues where various contribs or other packages require a certain php version/name to be installed.