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The Manaphy code worked just fine for me.
Re-Battle Regigigas (L+R)
94000130 fcff0000
b21c4d28 00000000
b0000004 00000000
20001294 00000000
d2000000 00000000
This works in Diamond. It might work for Palkia in Pearl, but I do not have Pearl so I can not test.
Re-Battle Dialga
94000130 fcff0000
b21c4d28 00000000
b0000004 00000000
20001138 00000003
20001273 00000000
20001284 000000c9
d2000000 00000000
This code also allows you to re-battle Darkrai, Shaymin, and Cresselia. Ichapokemr, we bow down to you. We will bow down even further if you happen to have the code to let us re-battle Dialga/Palkia...