OK to mix Tamiya regular and extra thin cements?

Is it OK to mix Tamiya regular and extra thin cements? I use the Xtra thin most of time, but for some applications I need a slow-drying cement. However, I find the Tamiya regular cement too thick.

I don’t see why not, however the thicker the cement means it will leave glue marks if you get some outside the joint. That means make sure the seam is accessible to sand easily.