We currently have only 1 DHCP scope using dhcp reservation. We will be dividing up our current network (10.10.x.x/16) into multiple subnetworks (10.10.x.x/24) so we'd need to create a multiple dhcp scopes (each with its own default gateway) in dhcpd.conf file.
We're planning to copy the option lines for each scope and edit it accordingly.

Below is the sample of our current dhcpd.conf:
option domain-name "company.com";^M
option domain-name-servers 10.10.10.52, 10.10.10.2;^M
option time-servers time.company.com;^M
option netbios-name-servers 10.10.10.200, 10.10.10.201;^M
ddns-update-style none;^M
^M
^M
subnet 10.10.0.0 netmask 255.255.0.0 {^M

deny unknown-clients;^M
^M
default-lease-time 86400;^M
option subnet-mask 255.255.0.0;^M
option routers 10.10.10.1;^M

host XP {
hardware ethernet 00:00:7F:BA:8C:85;
fixed-address 10.10.20.221;
}
host MAC {
hardware ethernet 00:0E:7F:BB:6F:8G;
fixed-address 10.10.10.235;
}


We're planning to do something like below:
#scope for 10.10.10.0/24
option domain-name "company.com";^M
option domain-name-servers 10.10.10.52, 10.10.10.2;^M
option time-servers time.company.com;^M
option netbios-name-servers 10.10.10.200, 10.10.10.201;^M
ddns-update-style none;^M
^M
^M
subnet 10.10.10.0 netmask 255.255.255.0 {^M

deny unknown-clients;^M
^M
default-lease-time 86400;^M
option subnet-mask 255.255.0.0;^M
option routers 10.10.10.1;^M

host MAC {
hardware ethernet 00:0E:7F:BB:6F:8G;
fixed-address 10.10.10.235;
}

#scope for 10.10.20.0/24
option domain-name "company.com";^M
option domain-name-servers 10.10.10.52, 10.10.10.2;^M
option time-servers time.company.com;^M
option netbios-name-servers 10.10.10.200, 10.10.10.201;^M
ddns-update-style none;^M
^M
^M
subnet 10.10.20.0 netmask 255.255.255.0 {^M

deny unknown-clients;^M
^M
default-lease-time 86400;^M
option subnet-mask 255.255.255.0;^M
option routers 10.10.20.1;^M

host XP {
hardware ethernet 00:00:7F:BA:8C:85;
fixed-address 10.10.20.221;
}

Is this the correct way to do it?

Thanks.

you wouldn't redefine the same global options multiple times, just the subnet { } data. other than that, seems good.

a deny unknown-clients option makes dhcp VERY intensive to administer... you are aware of that right?

Yes, we've been using "deny unknown-clients" for years and we're used to it now.
So like this then? Leave the global options and just specify the subnet and the rest for each subnet (default gateway and even mask in some subnets will be different)?

option domain-name "company.com";^M
option domain-name-servers 10.10.10.52, 10.10.10.2;^M
option time-servers time.company.com;^M
option netbios-name-servers 10.10.10.200, 10.10.10.201;^M
ddns-update-style none;^M
^M
^M
#scope for 10.10.10.0/24
subnet 10.10.10.0 netmask 255.255.255.0 {^M

deny unknown-clients;^M
^M
default-lease-time 86400;^M
option subnet-mask 255.255.0.0;^M
option routers 10.10.10.1;^M

host MAC {
hardware ethernet 00:0E:7F:BB:6F:8G;
fixed-address 10.10.10.235;
}

#scope for 10.10.20.0/24
subnet 10.10.20.0 netmask 255.255.255.0 {^M

deny unknown-clients;^M
^M
default-lease-time 86400;^M
option subnet-mask 255.255.255.0;^M
option routers 10.10.20.1;^M

host XP {
hardware ethernet 00:00:7F:BA:8C:85;
fixed-address 10.10.20.221;
}