I've checked your procedure. This similar to one that I've used with the old linuxmce 0704 release for upgrading the slimserver from 6.2.2 to 6.5.4.
But the actual 6.5.4 deb package is structured in different mode. And could be necessary to change many scripts files for the starting and stopping processes.
The possibility to create a new .deb package would be a great solution, also for the dependences for these packages pluto-slim-server-streamer and pluto-slimserver-plugin that have the dependences from this one: slimserver (6.5.4 release).
Thanks for your support.