Under some circumstances, the answer is yes. For example, both Wisconsin and federal courts have permitted police to conceal their identities (i.e. undercover stings) to gain entry to a home. The same goes for posing as a trash collector to gather evidence from someone’s home. On the other hand, courts don’t allow police officers to lie about whether or not they have a warrant or other lawful authority to gain consent to search.
However, the Wisconsin Supreme Court has not definitively ruled whether police officers can lie about the purpose of their investigation to gain consent to search. For example, it is unclear whether an officer can get you to agree to submit a DNA sample by saying the search is intended to clear you of a robbery when the officer is actually investigating an assault. In addition, trial courts have condoned this sort of conduct. Bottom line: if you agree to a search you should be prepared for the possibility that the police will try to use any evidence they find for any purpose they want, even if they tell you it will only be used for a limited purpose.