So it should work, although I don't know how DA would react to it as we only used the customapache script, not DA itself (not possible in intranet environment behind a NAT).
How do you mean ?
I did:
cd /usr/local/directadmin/customapache
./build update
wget'ed latest .tar.gz of php 5
vi build
changed PHP version number to 5.0.4.
and did a ./build all.
Note: there was no earlier version of PHP or apache installed.