That comment of Rash"i is quoting from the G'mara (Sanhedrin 86), which derives that [although the words plainly mean "do not steal"] based on the hermeneutic device called davar halamed me'inyano. The context of capital crimes in which "lo signov" appears implies that it too must be the capital crime of kidnapping. The meaning of the pasuk is therefore slightly different (i.e. more specified) than the meaning of the words de(or re)contextualized. The verb ג.נ.ב is certainly still available (especially to a poet) for its broader meaning of "steal".
In fact, the same g'mara that derives the specification of "lo signov" meaning "do not kidnap" derives the specification of the almost identical pasuk "lo signovu" meaning "do not steal [things]".