ip static route, make changes permanent/persistent upon reboot

Yes. Add the line:

123.456.7.89/32 via 192.168.10.101 dev eth1

to /etc/sysconfig/network-scripts/route-eth1 as shown here.

While this answer works, the current preferred format for /etc/sysconfig/network-scripts/route-ethX is:

GATEWAY0=10.156.196.1
NETMASK0=255.255.254.0
ADDRESS0=10.156.248.0
GATEWAY1=10.156.196.1
NETMASK1=255.255.254.0
ADDRESS1=10.156.244.0

Be sure to increment the value of the numeral when you add a route.

Unfortunately, the new preferred format of GATEWAYX:/ADDRESSx:/NETMASKx:/ makes it harder to programmatically add static routes via the older format of 192.168.1.0/24 via 10.1.1.1. It can be worked around, but adds unnecessary complications to scripting routes.