The Dui and Ren channel are always open however you can have spots blocked. What you are refering to is passing more Qi thru the 2 channels. In order to do this you need to generate and gather more. You should not favor any technique to do Xiao zhou tian or even Da zhou tian. If you practice correctly you will find there really is no technique to do to accomplish this. This is why Liu I Ming wrote" 那些总想着永生的人，反而更接近死亡。 If you do not know understand what this says you should seek out a qualified teacher.
I really do not see "opening" the dui and ren channel hurting unless there is a severe blocking in the channel "Bu tong ze tong" 不通则痛 I think in my opinion if there is block in the channel you should see a TCM doctor first than have a teacher guide you thru the process.