Good question. In my opinion there's no reason to consider this an emergeny coinage. They just uniformized the bronze coinage already in circulation with new face values. The large bronze 80 reis was countermarked (40) and this is a very common coin. I have four of them, including this stunning example:

Sorry — could not resist the temptation of showing it again!
Note that the Krause Catalogue 1801–1900 does not make a distinction between regular and emergency issues for these, i.e. the (10) / (20) / (40) countermarks; they're just countermarked coins. I just checked a number of these coins in the Numista catalogue and they're mostly tagged as emergency coins, which I think is a mistake.
As I write I'm looking at the book by F. Dos Santos Trigueiros, Dinheiro no Brasil (2nd ed. 1987). He has a chapter on emergency coinage and on p. 138 he claims that the first emergency issues in independent Brazil was in 1838.
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