Data type OID numbers fixed?

I'm in the process of finishing a native Protocol 3 PostgreSQL driver
written in Pike.
And while trying to make it make intelligent decisions regarding binary
or text encoding of different columns and parameters, I run into the
OIDs of types.

In looking through the specs, I decided that the following OIDtypes will
be (automatically) binary passed (both as results and as parameters),
all others will be passed as text:

case 16: // _bool
case 17: // _bytea
case 18: // _char
case 20: // _int8
case 21: // _int2
case 23: // _int4
case 25: // _text
case 142: // _xml
case 829: // _macaddr
case 869: // _inet
case 1042: // _bpchar
case 1043: // _varchar
case 1700: // _numeric
case 2950: // _uuid

How large is the probability of these numbers ever changing?
Should I extract them from a query at the beginning of the connection?
Or can I leave them hardcoded in the driver?
--
Sincerely,
Stephen R. van den Berg.

A truly wise man never plays leapfrog with a unicorn.