Font directive effect seems to be position dependent.

[seisiuneer]

%%textfont just before %%text in the header appears to have no effect, but if it's added at the top just below the X: tag, it works. Actually on further testing, anywhere in the header works. Once you're out of the header, %%textfont doesn't work.

For example:

X: 1
T: Cooley's
C: Traditional
R: Reel
M: 4/4
L: 1/8
Q: 1/4=90
K: Edor
%%textfont Times-Roman 24
%%text Hello world
|:"Em"EBBA B2 EB|B2 AB dBAG|"D"F/E/D AD BDAD|F/E/D AD BAGF|

doesn't reflect the textfont change but:

X:1
%%textfont Times-Roman 24
T: Cooley's
C: Traditional
R: Reel
M: 4/4
L: 1/8
Q: 1/4=90
K: Edor
%%text Hello world
|:"Em"EBBA B2 EB|B2 AB dBAG|"D"F/E/D AD BDAD|F/E/D AD BAGF|

does.