There is a story told in Y'shivot
A Hossid will give you
15 answers to a single question
A Litvak will give you a single answer to 15 questions.
Here are two related knotty problems
In Hayyei Sarah, Eliezer - "Eved Avraham" is assigned to find a mate for Yitzchak. The Talmud admonishes us that his technique involved "Nichush" so we should NOT do it. This begs the question how could Eliezer use this means to select a proper shidduch? Alternatively, how can it be that the great match for Yitzchak was manifested using such "under-handed" means?
Similarly in Toldot, Yaakov "usurps" the brachah from Esav via deception. One may not violate Halachah on the say so of a parent, so obedience to his mother is no excuse. So how was Yaakov permitted to engage in such a masquerade?
My approach is similar and simple. In each case, the alleged offense was committed under the instruction of a Prophet/Prophetess; and Scripture actually makes this quite clear on a P'shat level
In the case of Eliezer he is told by Avraham that a Malach will accompany him and that Hashem will cause him to succeed. Given this CONTEXT, his Nichush was under Divine Providence and therefore did not involve superstition or "dark forces"
Similarly, Rivka was told by Hashem [directly so - if we set aside Rashi] that "Rav Yaavod Tsa'ir." Given that this n'vuah is also in the text, her command to Yaakov is therefore that of a prophetess and not simply that of a Mom. Yaakov is therefore engaged to commit this deception in this extraordinary circumstance.
This also explains why the text juxtaposes these Prophetic pronouncements immediately prior to the questionable behaviour, in order to set up a proper context so that we would not mis-understand the dynamic here and learn the wrong lessons re: Nichush and deception