I'm wondering if it's possible or acceptable for foreigners to use 漢字 to write their names that would usually be written in カタカナ. I know that some names are already Japanese names such as Ben【勉】, Mary【茉莉】, etc., but is it possible to use common 音読み to extend this kind of thing further?
For example, maybe Ben【勉】could be extended to Benjamin【勉邪民】, or Thomas could be written as【斗枡】. Would this type of thing be acceptable or understood, or is it simply more practical to use the カタカナ versions?
For Western names, practically speaking, Katatana is best. If you're a citizen of a country where Kanji is used on official documents like your passport, say... China or Korea, then it is common to use either Kanji or Katakana in Japan.
For citizens of Western countries, your Kanji name will never be your "official" name (unless you become a citizen of Japan, Korea, China, etc.) Almost all Japanese institutions commonly handle alphabetic names at this point, so even your Katakana name may not be used on official Japanese documents.
However, some people use a Kanji-fied version of a Western name for their hanko/inkan, and this is usually acceptable even in government and banking documents.
So if your name is "Benjamin Button" you could register a hanko/inkan with your city office or bank with 「勉邪民 牡丹」 on it. As long as there is some clear link between the Kanji and your name, you most likely wouldn't have any trouble.
