MSP ATC reports directives are not complied with when aircraft land with a tailwind on a runway which is not bare and dry.

Narrative

When I signed on to Local; the relieved controller stated during the brief that wind was 2507; we were landing Runway 12R. Weather was 1 3/4 miles vis and snow; braking action was good first half of runway fair second half of runway. The runway was not bare and dry. I informed the Front Line Manager (FLM) that we had a tailwind to a contaminated runway (again not bare and dry). The FLM attempted to coordinate with the TRACON for a runway change and was apparently told that we would change at some time and that they would call him back. It took approximately 30 minutes to finally make the runway change to 30L/R; during that time I issued landing clearance to approximately 10 aircraft on Runway 12R; with a tailwind and a contaminated runway; all aircraft were given a wind checks. This was a violation of FAA order 8400.9 para 7(d)(2)(b); given that the runway was not bare and dry and a tailwind existed; I should not have issued a landing clearance to these aircraft and instead should have canceled their approach clearances and taken them off the final. This is a routine situation at MSP/M98; we routinely allow aircraft to land when weather and runway conditions change in violation of the above stated order. When similar situations occur in the future; approach clearances should be canceled and vectors given to the aircraft to a runway not in violation to the above stated order.