Can I buy a simcard in Yangon without presenting my passport and if yes, where and which?

Unlikely, because as of 31st March 2017, all SIM cards have to be registered.  There has been a campaign (in English and Myanmar-sa) over the past few weeks to get everyone to register their SIM cards, either online or at the mobile network customer centres, with 'dire warnings' of the illegality if one doesn't register one's SIM card....