Since you said it 3 days in advance .. you have some merit on upholding the rule. HOWEVER, the 2 guys must admit to at least knowing of the rule change prior to draft.
Overall, I don't think their strategy should be penalized. I have done similar things in the past and people got mad. If there are no max moves per week or per season, then it is fully within the rules. If that strategy works, then the rest of the league can go ahead and drop their D and try and grab available forwards on the FA list too, its fair game. Everyone has their own strategy and as long as it doesn't break rules, its fine.
But you are stuck in a hard place now, because you need to prove that every owner was aware of this rule change prior to draft in order to uphold this rule. 3 days was kind of short notice, but if the 2 guys admit to knowing, and the rest of the league likes the rule, then I say keep it.
1 Year H2H (G,A,+/-,PPP,GWG,PIM,Hits, SOG,W,GAA, SV%,SHO), 8 Teams 3C, 3LW, 3RW, 3F, 6D, 3G, 4 Bench, 2 IR
C: M.Koivu, Sharp (LW), Stepan
LW: Perron (RW), Soderberg, Landeskog
RW: Ovechkin, Carter (C/LW), Skinner (C/LW)
F: Simmonds, Johansen, Anisimov
D: Doughty, OEL, Franson, Gudas, Enstrom, Daley
G: Price, Varlamov
BN: Stempniak, Perreault, Lee, Michalek, Maroon
IR: Letang
Lost to Injury: Tavares, M.Smith, Dupuis, Fowler, Parenteau, Kreider, Granlund, Lupul, McDonagh