I can confirm that running two user commands with variations of tbone's SelectEx Script Addon from a button doesn't work. Only the first one will be executed. Here are two examples:
User command 1:var cmd = DOpus.Create.Command
var jsFilter = ""+
"if (item.metadata == 'audio'){ "+
"var year = new String(item.metadata.audio['mp3year']);"+
"var int = parseInt(year);"+
"if (int < 1980) return false;"+
"}";
cmd.RunCommand('Delete coll://Oldies REMOVECOLLECTION=auto QUIET')
cmd.RunCommand('SelectEx LINEAR '+
'PATH="'+DOpus.FSUtil.Resolve('/mymusic')+'" RECURSE JSFILTER="'+jsFilter+'" '+
'ITEMCOUNTPERC=100 '+
'COPYTOCOLL=Oldies '+
'TOFILE="'+DOpus.FSUtil.Resolve('/temp\\Oldies.m3u')+'" '+
'COMMANDS=Go coll://Oldies')
cmd.RunCommand('Set SORTBY=+mp3year(0)')
User command 2:var cmd = DOpus.Create.Command
var jsFilter = ""+
"if (item.metadata == 'audio'){ "+
"var genre = new String(item.metadata.audio['mp3genre']);"+
"if (genre.indexOf('Pop') !=-1) return false;"+
"}";
cmd.RunCommand('Delete coll://PopColl REMOVECOLLECTION=auto QUIET')
cmd.RunCommand('SelectEx LINEAR '+
'PATH="'+DOpus.FSUtil.Resolve('/mymusic')+'" RECURSE JSFILTER="'+jsFilter+'" '+
'ITEMCOUNT=1000 '+
'COPYTOCOLL=PopColl'+
'TOFILE="'+DOpus.FSUtil.Resolve('/temp\\PopColl.m3u')+'" '+
'COMMANDS=Go coll://PopColl')
cmd.RunCommand('Set SORTBY=+mp3genre(0)')