On the pre-1000 AD date of the text, cf.
P. K. Gode, "Date of Rākṣasa Kāvya or Kāvyarākṣasa — Before A.D. 1000", In: Studies in Indian Literary History vol. 1, pp. 195-202;
orig. publ. in Journal of Indian History, Madras, vol. 19/3, 1940 pp. 312-319+ Indology list in last October for more references.
Note that the vār- stem, even if a bit archaic, is nor less classical than the use of nṛ- : both are given as paradigms in traditional manuals like the Siddharūpam (cf. also in Hanxleden's Grammatic Grandonica) and also used in yamaka poems by Vāsudeva (the possible son of Ravideva, both probably poets at the court of the Cera Perumals of Mahodayapuram in the 9th-10th centuries AD).
Best wishes,
Christophe