closed am190 by mistake

I don't know of any way around this one. You also have to concider even if you can restore AM from a back up, it could have effected other programs like GL system control records.

I know with December it is not the best time to have this happen since many companies are calendar year end and you want the last month to be clean but you may want to start thinking of how to reconcile the month and use auto reversing JE's to adjust your balances and catch up in January.

There is no way to reopen a closed period. I would not recommend using "partial" restore to force the system into thinking the period is open, just too risky in my opinion.

I would just process with your current open period. You can add asset with closed-period-in-service date. You can change the date on JE so it will send to GL with the closed period date also.