You can use USE statement in stored procedure in dynamical SQL like

CERATE PROCEDURE [dbo].[USE_PROOV_KUIDO_S]

@baas NVARCHAR(128)=NULL

AS

BEGIN

SET NOCOUNT ON

DECLARE @er NVARCHAR(1000)

SET @er='USE ['+ISNULL(@baas,DB_NAME())+'];SELECT NAME FROM SYSUSERS WHERE ISSQLUSER=1 AND HASDBACCESS=1'

EXEC (@er)

END

EXECUTE [dbo].[USE_PROOV_KUIDO_S] @baas='MSDB'

EXECUTE [dbo].[USE_PROOV_KUIDO_S] @baas=NULL