Is there a usage for  as "rèn"? Is there a usage for   as "rèn" ? I cannot find examples with this pronunciation.
I understand the usages as yáng, jiāng, &amp; qiāng, as explained by  dROOOze and others in what-is-the-top-part-of-姜.... However, the unicode pronunciation for  U+2634C is given as rèn, and WIKIPEDIA includes rèn without examples  Etymology 2)
re: [⺷ U+2EB7 /  U+2634C]

[added] I found one reference / usage here, "补字如甚切音姙..."  but I have no skill to read it and understand if it is using  or discussing it as 'suspicious'. The site notes that the text was OCR'd and is unedited.
No.
「」 has no usage examples as the reading rèn (Bopomofo: ㄖㄣˋ). Note that many ancient dictionaries make definitions up out of thin air, which is why quotes from character usage in literature is so important.

At least one dictionary author, smelling something fishy was going on, said


《字彙補》
...疑「」字之譌

Suspected to be a corruption of 「」 (rěn).

So it might come from 「」 with a horizontal line added to the bottom.

Further reading
See the reference given by Wiktionary: Dictionary of Chinese Character Variants (教育部異體字字典), A03215-002