Word for “decorated too much”

Solution 1:

I don't know of any better single verbs than overdecorate, overornament or overembellish. Bedizen is good if you don't mind obscure. I might be tempted to coin baroquify. Related, possibly useful phrases include to tart [something] up and gilding the lily.

Solution 2:

Adjectivally, you could describe something as baroque:

extravagantly ornate, florid, and convoluted in character or style
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or florid:

flowery; excessively ornate; showy
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Verbwise, I can't think of any single word that encompasses that extent of a description, unless you want to go for something like overembellished with an additional phrase to point out how far beyond the pale it's gone: "He had overembellished it to the point that it became a grotesque parody of its potential nature", or "he had embellished it well past the point of baroque floridity."