UDP 1434 is for the SQL Monitor service.  SQL Server (the database
engine) listens for connections on various TCP ports (the default being
1433).  The monitor service is for translating connection requests for
SQL instances (which may be named instances) into TCP port numbers (or
particular named pipes) essentially.  If you're using static TCP ports
for your SQL Server instances (whether they're named instances or not)
then you don't need the monitor service running because you already know
what TCP ports to connect on and they don't change.  (It's a different
story if your SQL instance(s) is using dynamic ports, then you need the
monitor service.)  If you're using static TCP ports then your SQL
clients simply connect to the SQL instance using its TCP port number
(eg. tcp:myserver,1433) and, in fact, this is what you need to do if
you're routing connection requests through a firewall (unless you open
up masses of incoming TCP ports on the firewall in which case you may as
well not have one).

So, to answer your question, no you cannot change the UDP port that the
SQL Monitor service listens on.  However, you can turn off the monitor
service, block UDP traffic on 1434 and get your SQL clients to connect
using specific TCP ports as required if your SQL instances are using
static TCP ports (rather than dynamic).  This is a more secure setup
anyway (although all the known 1433 & 1434 exploits, the most (in)famous
being slammer & blaster, have been fixed in SP3/SP3a from memory).

--
*mike hodgson*
http://sqlnerd.blogspot.com

No...the SQL Server Resolution Service is set to use UDP
1434.
You can have the clients specify port numbers that they need
to use to connect to instances. In that case, you don't need
to keep that port open. The port can be specified in the
applications connection string or you could create an alias
on the client and specify the port number there.

-Sue