>Is there any evidence in the suttas showing the Buddha was "flexible" in his teaching of Dhamma?

He was not a little flexible when one spoke A-dhamma but did not limit the Tataghata to his speech at the same time, as the only that should be taken as that of the Tataghata.

Once the Budddha rebuked some who told that another does teach something the Buddha did not say by "What ever Dhamma a Noble one speaks, it is the Dhamma of the Tatagatha". One may google it ... or ask a monk for details if able to leave house. It was, btw, on the teaching one gave, that one should seriously reflect one's own attainments and that of others, periodical!

*[off (ordinary) cause: this is not given for trade, stacks, exchange or Buddh-ism and other binding purposes for the world but dedicated for refuge toward liberation]*