Well Pilgrim, looks like you’re not the only one interested in this 
There are two issues with mixing different formats:
1/ If the T5577 frontend and encoding settings are strictly identical between tag type A and tag type B (i.e. if only the format of the bit sequence changes) AND both sequences fit in the T5577’s memory, then yes, you can encode both on the T5577
2/ BUT! The big issue is: will the reader for which the second sequence is intended be forgiving enough to ignore the first sequence if doesn’t undertand it, and will it manage to correctly latch onto the beginning of the second one?
The tests I conducted to assess the viability of the hack show that at least all of my EM readers are highly intolerant of stuff they don’t understand coming through: they all want the transmission to start with 9 preamble bits exactly, either when something enters the field for the first time, or following a valid previous transmission. Any spurrious byte inserted anywhere in the sequence renders the readers silent. In short: they detect something is off and refuse to interpret the rest of the sequence.
So the reply is… it depends. If you’re lucky and the target reader for the second UID is very forgiving (and probably quite smart too, to sort out garbage from a valid transmission with only a few bytes from a weakly protected protocol), then yes. Most likely, you won’t be lucky. But it doesn’t kill to try it.
The EM-with-EM UIDs trick works because EM tags were designed to send the same sequence back-to-back from the get-go, and all EM readers expect this. But EM readers never expect two different tags with different protocols to talk politely one right after the other in sequence. That never happens in real-life.