When a verb in the present expresses the past, is it CORRECT to conjugate it to the past and still nothing changes?


If

> あの子どもは、それを口に **入れる** や、吐き出した

is correct, is

> あの子どもは、それを口に **入れた** や、吐き出した

also correct? If yes, has the meaning changed at all?




(Updated to fold in feedback from Chocolate in the comments.)

The や here ~~appears to be a shortening of~~ is equivalent to the や in the set
construction ～や否【いな】や ( _~ ya ina ya_ , "as soon as ~"). The single や means
roughly the same thing ("when ~, at the time of ~"). The や construction
grammatically requires that the preceding verb be in the 連体形【れんたいけい】 (
_rentaikei_ , "attributive form" used to modify a noun), which in modern
Japanese is identical to the so-called "plain form", "dictionary form", or
終止形【しゅうしけい】 ( _shūshikei_ , "terminal or conclusive form" used predicatively,
such as at the end of a sentence).

Consequently, your second sample sentence would not be considered correct
grammar.

When translating into English, we would indeed use the past tense form of the
verb, such as _" No sooner had that kid **put** it in his mouth, when he threw
up."_ or, _" That kid **stuck** it in his mouth and immediately puked."_, etc.

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Please comment if the above does not address your question.

