𐑐𐑤𐑱𐑡𐑽𐑦𐑟𐑩𐑥 → 𐑐𐑤𐑱𐑡𐑼𐑦𐑟𐑩𐑥

[mwgamera]

It seems that plagiarism & plagiarist should be spelt with 𐑼 rather than the etymologically motivated 𐑽, just like the related verb plagiarise/plagiarize and its forms.
OED shows an optional /(ɪ)/ in parens for RP; Cambridge has the pronunciation with /-dʒi.ə.rɪ-/ (US /-dʒi.ɚ-/), but listed secondary to the one with /-dʒ^ər.ɪ-/ (US /-dʒɚ.ɪ-/). M-W lists it as "also -jē-ə-" giving preference to plain "-jə-ˌri-". Other sources don't even consider any other possibility than /-dʒərɪ-/ which seems to be more common pronunciation across the board (idk about Australian, though). All the sources I checked transcribe the stems of the -ism & -ist nouns identically to the related verb.

So it looks that it should be:

Latn	Shaw	POS	IPA
plagiarism	𐑐𐑤𐑱𐑡𐑼𐑦𐑟𐑩𐑥	NN1	ˈpleɪdʒərɪzəm
plagiarisms	𐑐𐑤𐑱𐑡𐑼𐑦𐑟𐑩𐑥𐑟	NN2	ˈpleɪdʒərɪzəmz
plagiarist	𐑐𐑤𐑱𐑡𐑼𐑦𐑕𐑑	NN1	ˈpleɪdʒərɪst
plagiarists	𐑐𐑤𐑱𐑡𐑼𐑦𐑕𐑑𐑕	NN2	ˈpleɪdʒərɪsts