In the next release (6.52 which should be released tomorrow after a bit more testing), you will be able to define New Years the way you are asking in a couple of ways:
# Saturday
1*1:0:1:0:0:0*NBD,BD1,IBD,FD1 = New Year's Day
# Sunday (observed Monday)
1*1:0:1:0:0:0*NBD,BD1,NBD,FD2 = New Year's Day
# M-F
1*1:0:1:0:0:0*IBD = New Year's Day
or
# Saturday
1*1:0:1:0:0:0*IW6 = New Year's Day
# Sunday (observed Monday)
1*1:0:1:0:0:0*IW7,FD1 = New Year's Day
# M-F
1*1:0:1:0:0:0*IBD = New Year's Day
It's important to name the holiday the same for all definitions.