If I understand correctly, the NS_X and A-MPR (additional maximum power reduction) are the parameters taken from 3GPP TS 36.101.
All power related parameters (except transmit power commands), are provided to the UE with the use of RRC signalling (see 3GPP TS 36.331).
RRC IE (information element), that directly relate to A-MPR (from TS 36.101) is called additionalSpectrumEmission (in RRC specification, i.e. TS 36.331). It is present in:
SystemInformationBlockType2 (see TS 36.331, section 6.3.1)
and as a part of MobilityControlInfo that is an IE present in RRCConnectionReconfiguration message, used for the purpose of Handover Command.
The network provide A-MPR:
to all the users in a particular cell (idle and connected), by broadcasting system information;
during Handover Procedureto the handed-over UE within RRCConnectionReconfiguration message, so that UE knows, what are the power settings / limitations in the target cell.