Can "puisse" replace "pût" in "j'avais le droit... d’attendre que mon avocat pût m’assister"

Question

The question is on pût in this excerpt from L'Étranger by Camus.

Peu de temps après, j’étais conduit de nouveau devant le juge d’instruction. Il était deux heures de l’après-midi et cette fois, son bureau était plein d’une lumière à peine tamisée par un rideau de voile. Il faisait très chaud. Il m’a fait asseoir et, avec beaucoup de courtoisie, m’a déclaré que mon avocat, « par suite d’un contretemps », n’avait pu venir. Mais j’avais le droit de ne pas répondre à ses questions et d’attendre que mon avocat pût m’assister. J’ai dit que je pouvais répondre seul. Il a touché du doigt un bouton sur la table. Un jeune greffier est venu s’installer presque dans mon dos.

Question

Would it be ungrammatical to replace this pût with puisse?

Background

I am expecting the answer that the sentence would remain grammatical after the replacement and also continue to mean the same thing. The only difference would be in the reference time frame. puisse would be framed by the time of magistrate's speaking (thus the lawyer becoming able is a hypothetical situation to obtain, if it does, at a future relative to the time of the frame); whereas pût would be framed by the narration of the quoted block of sentences themselves (thus the same event, the lawyer becoming able, is in a relative past to its frame). There was a discussion of time frame in this earlier post. (See answer by Stéphane Gimenez.)

Answer 1

I suppose I should have done this quick research before posting a question.

Apparently, the replacement is permissible because, according to the sources below, the replacement of imperfect subjective with present subjective is always permissible.

I might add that French subjunctives, then, seem to behave differently from English or German subjunctives but rather like English indicatives, in the following sense.

English and German subjunctives are unaffected by the tense of the main verb in whose context they occur. For example:

It is required that the child be accompanied by an adult at all times.

It was required that the child be accompanied by an adult at all times.

At least in formal writing, French subjunctives change to "match" the tense of the main verb as do English indicatives. For example:

Je préfère que vous arriviez à temps.

Je préférais que vous arrivassiez à temps.

I am posting this answer so any error in my understanding can be pointed out.

Sources

Wikibooks:

The subjunctive imperfect is very rarely employed in French; generally it only appears in literature and is viewed as archaic. It can in all instances be replaced by the subjunctive present. The subjunctive imperfect is employed in any instance in which the subjunctive is required, provided the trigger verb is in a past tense. In the example "Il fallait que le garçon allât à l'école", the subjunctive trigger verb "falloir" is in the imperfect, thus "aller" has been conjugated in the subjunctive imperfect. French speakers would normally express this as "Il fallait que le garçon aille à l'école", where "aller" has been conjugated in the present subjunctive.

Lawless French:

The imperfect subjunctive is used in a subordinate clause when the main clause is in the past. Its non-literary equivalent is the present subjunctive.

Answer 2

Indeed the subjunctive past tenses are nowadays only used in litterature and have become kinda obsolete in oral. Whereas the other romance languages have kept using them (Spanish, Portuguese, Italian people use them naturally in everyday's life) the subjonctif imparfait and subjonctif plus-que-parfait are never used when speaking, so that they are even ignored by some French people, but knowing those tenses is an obvious proof of your knowing of the language! So yes the only tense used orally with the subjunctive mode is the present, even in the cases where imperfect subjunctive would fit better.

Answer 3

pût is subjonctif imparfait.

The subjonctif imparfait is used to tell the story, actions that advance the story.

You can't use subjonctif présent.

The present subjunctive is used to express present actions or ideas which are subjective. It is nearly always found in dependent clauses introduced by que or qui, and the subjects of the dependent and main clauses are usually different.