I'm not an expert in Texture but i can give you my point of view.

In HCP, since the structure is very complex, more than CFC or BCC, strain hardening greatly depends on the slip modes (prismatic1, prismatic2, basal, pyramidal1, pyramidal2 ...) present in HCP. Interactions between these slip mode greatly reorient each crystal in an HCP polycrystalline aggregate depending on the plastic activity, the acting slip modes and the level of strain/stress induced also depending on applied the stress direction (some grain may more favourable to reorientation than others).

So, to quantify that orientation depending on the strain hardening in HCP, you can use experimental procedure to follow the evolution of the angles between each slip and the test tube direction for an in-situ test or after every step of a test. To do it you first need to identify your slips. EBSD is an excellent tool for that and is widely used. You can also use the schmid factor which can be measured or calculated from experiment data. Using diffraction you can also show pole figures which is another way to quantify your orientation dependant strain hardening.

Briefly, the principle is that since the grain is reoriented because of strain hardening due to plastic activity, the intensity of the diffracted light (EBSD, Diffraction ...) received by the detector will change during the test.  You will be able to observe the variation of diffraction peak on the diffractogram (between the start and the end of the test). From that you can also quantify your reorientation.

You can check these articles and links which may helps you understand better.

Gert Nolze can also give a better answer about those experimental procedures.

I hope it helps you.

Greetings

Article Intergranular Strain Evolution in Titanium During Tensile Lo...

Article Experimental and theoretical studies of intergranular strain...

Conference Paper Development of internal strains in textured Titanium alloy d...

Conference Paper Fundamentals and applications of EBSD