Hi @Danchyg1337, thanks for reaching out us.
With regard to your question, I'm a bit confused because iso-parametrics are actually lightweight representations of geometrical elements which being governed by parameters can be drawn using curves defined by the driving parameters having the same value.
This usually applies to rational and non-rational surfaces where the s and t parameters can represent s and t iso-parametric curves defined by the locus of points characterized by the same parameter value.
In the case of a generator, this is meaningful because, depending on the math behind the generator, you could take advantage of the iso-params representation but for a modifier I really don't get it. Usually modifiers when applied in a representation where iso-params are shown, automatically deform the isoparametric curves (check for example applying the bend deformer to a sphere represented via iso-params)
Assuming that the code you've posted is running in a BaseObject::ModifyObject() method then BaseObject::SetIsoparm() can not be called from there.
Finally, to my knowledge, deformers like the Bevel Deformer does nothing with regard to iso-params representation since being it applicable only to polygon objects iso-param representation coincides exactly with the edges representation.