Replaces xsl_mod's leading parameter values with params, matched by
position (not by name) – e.g. a raw numeric vector such as DEoptim's
bestmem. The result keeps xsl_mod's original parameter names.
Details
params may be shorter than xsl_mod$params, in which case only the
first length(params) parameters are replaced and the rest keep their
existing values. This is what lets xsl_fit() optimize a leading subset
of a model's parameters (e.g. uncfam()'s numeric X/B/C but not its
categorical variant) by giving DEoptim lower/upper bounds shorter
than the model's full parameter list.