Question: That is, what is the standard way to tell a string player to play normally again?

Answer: 
You can use **ordinario** or **normale**:

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> **ordinario or normale**: to bow in the ordinary or normal fashion, canceling a previous instruction to play s.p. or s.t.
>  abbreviations: ord. ; norm.; N. - [source](http://www.moderncellotechniques.com/bow-techniques/ponticello-tasto/ponticello-tasto-overview/)
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'loco' is also used in these situations.