No, not basic.

Testing programme changes universal rating for nothing, harking back to a classic swell (5)

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There’s a charade, letter substitution, abbreviation, charade letter, reversal indicator…

The whole def harks back to older definitions.

No, not relic.

It’s a word that was in vogue with this particular definition during 17th and 18th century in particular. It is still in common use but with a more common definition.

The charade for this word is also in use today but again, the definition I’ve used is an older one in vogue in the Roaring Twenties, 30s, 40s…

Testing programme changes universal rating for nothing, harking back to a classic swell (5)

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There’s a charade, letter substitution, abbreviation, charade letter, reversal indicator…

The whole def harks back to older definitions.

Not solid.

Testing programme changes universal rating for nothing, harking back to a classic swell (5)

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Let me add a second cryptic clue:

I’ve heard both of the mouth adorn Dutch fields (5)

More…

Testing programme changes universal rating for nothing, harking back to a classic swell (5)

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testing programme [charade]
changes [letter substitution indicator]
universal rating [abbreviation] single letter
nothing [charade] single letter

harking back to [reversal indicator]