In addition to #1, the classical forms of the first two and the last two are かふ and かへる respectively, as in the dictionary. Also, 変える/換える and 帰る/返る have different pitch accents.
There are two different types of conjugation in (classical) 形容動詞(a kind of adjective), so-called タリ活用/ト・タル活用 and ナリ活用/ニ・ナル活用. ナリ活用/ニ・ナル活用形容動詞 changed to na-adjectives in modern Japanese.
e.g.
ナリ活用/ニ・ナル活用
遥かなる道のり(classical) - 遥かな道のり(modern)
道のりは遥かなり(classical) - 道のりは遥かだ(modern)
タリ活用/ト・タル活用
茫漠たる砂漠(classical) - 茫漠とした砂漠(modern)
砂漠は茫漠たり(classical) - 砂漠は茫漠としている(modern)
Almost all stems of タリ活用/ト・タル活用形容動詞 are Chinese compound words, and たり is originally from "a particle と + a verb あり" as same as a classical auxiliary verb たり. 堂々 can be used alone or in some compounds words (e.g. 威風堂々, 正々堂々), but thsese usages are not so many.
堂々たる and 堂々と are often treated as an attributive(連体詞) and an adverb in modern Japanese grammar, respectively.