I tested it. it does not reject but only get log. test below
R1 configuration below;
set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.1/24
set interfaces fxp0 unit 0 family inet dhcp vendor-id Juniper-vmx-VM5C9F5057B0
set routing-options static route 1.1.1.1/32 receive
set routing-options static route 1.1.1.2/32 receive
set routing-options static route 1.1.1.3/32 receive
set routing-options autonomous-system 12
set protocols bgp group ibgp type internal
set protocols bgp group ibgp export bgp
set protocols bgp group ibgp neighbor 192.168.1.2
set policy-options policy-statement bgp term 1 then accept
R2 configuration below;
set interfaces ge-0/0/0 unit 0 family inet address 192.168.1.2/24
set interfaces fxp0 unit 0 family inet dhcp vendor-id Juniper-vmx-VM5C9F50560F
set routing-options autonomous-system 12
set protocols bgp group ibgp type internal
set protocols bgp group ibgp neighbor 192.168.1.1 family inet unicast prefix-limit maximum 3
set protocols bgp group ibgp neighbor 192.168.1.1 family inet unicast accepted-prefix-limit maximum 2
root# run show bgp summary
Groups: 1 Peers: 1 Down peers: 0
Table Tot Paths Act Paths Suppressed History Damp State Pending
inet.0
4 3 0 0 0 0
Peer AS InPkt OutPkt OutQ Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
192.168.1.1 12 25 21 0 0 8:44 3/4/4/0 0/0/0/0
Mar 30 11:34:48 rpd[6797]: BGP_PREFIX_LIMIT_EXCEEDED: 192.168.1.1 (Internal AS 12): Configured maximum accepted prefix-limit(2) exceeded for inet-unicast nlri: 3 (instance master)
Mar 30 11:35:18 rpd[6797]: BGP_PREFIX_LIMIT_EXCEEDED: 192.168.1.1 (Internal AS 12): Configured maximum prefix-limit(3) exceeded for inet-unicast nlri: 4 (instance master)
Mar 30 11:35:48 rpd[6797]: BGP_PREFIX_LIMIT_EXCEEDED: 192.168.1.1 (Internal AS 12): Configured maximum prefix-limit(3) exceeded for inet-unicast nlri: 4 (instance master)
Mar 30 11:37:48 last message repeated 4 times