I don't know what the policy is at Chanmyay Yeikthā
nowadays, but you could try calling them.
This is what it says on the Mahasi Yeikthā site:
Foreign Yogis seeking admission should be ready and willing to undergo full-time Vipassana meditation for about six to twelve weeks which is considered and appropriate period of retreat for one to gain a basic knowledge and experience of Vipassana meditation.
There are plenty of other centres in Rangoon
and elsewhere that teach the Mahāsi Method — over 300 centres at the last count.
If you're planning on touring beyond the confines of Rangoon, I can recommend a visit to Mahasi Yeiktha in Taungyi, where the climate is much more tolerable.
Saddhamaramsi Yeiktha is another possible centre in Rangoon.