Timing may be tough since it's near X'mas/New Year

but if you can gamble, ONE-WAY
You can wait until 2-3 weeks before departure date, and EVA's YYZ-TPE should open up (if not, maybe YYZ-IAH/LAX/SFO/SEA/YVR-TPE would open), and it'll be easy layover (<24 hours) in TPE if you like before connecting EVA or SQ TPE-SIN


Otherwise you'll likely guaranteed to pay ONE $90+tax change fee to change your dummy return to something you like. But it may be worth it, if you change it 2-3 weeks out to change BOTH outbound AND inbound at once... it's up to you