Got it! In his book Rich and Rare Sean McMahon prints the song with the following comment:

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Tone is Coming Back again
Thomas Francis Mullan

A song which was part of the '98 Cantata written in celebration of the hundredth anniversary of the Rising. The cycle contained ten songs and was revived again in 1948 on the 150th anniversary.

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I'd never heard of the cantata.

Regards