Reference design more like "oh cool I like what they did here" as opposed to take the design and modify it. I'm pretty sure there is a different terminology but it escapes me at the moment.
I've heard 'particularized design' for minor changes, but we tend to make massive and significant changes, as well as minor ones. Slapping a giant radar on top of the mast for example, and changing an ASW platform to AAW come to mind.
Bunch of weird ones in JSS, like taking out a connecting structure between the two RAS posts for 'visibility', designing out the deck crane that enabled the containerized hospital setup, and extending the loading rail to both sides (vice just one) all had major structural implications.
You can also have code update type changes, if you use an older design, but given that we voluntarily comply to SOLAS anyway, we do have the option of not doing that if it's something significant. Generally actual warships exceed the SOLAS performance baselines anyway, so usually just updating equipment selection for different things does the job.
'Canadianizing' is probably a good catch all for taking a working, funcitonal design, trying to get it to do something radically different, changning all the components so you have to redesign the connection points, supporting structure and electrical/cooling systems, and randomly changing compartments around just because. T26 is a really solid base design, so we're relatively safe, but all the tradeoffs for adding massive weight up high is pretty interesting, and sure will cost us an absolute fortune and a lot of downtime as some of the exotic disimilar metals rust out in terrible to repair spots, but are required to cut weight.