No.. You have to make sure that the network is listed in mIRC's network list (aka server.ini)
If it's not listed, you'll have to add it first.
Here's the steps you need.
1) Open mIRC Options (Alt + o)
Only follow step 2 - 6 if you need to add the network. Otherwise go to step 7.
2) Select the Servers option under Connect
3) Click Add
4) Enter the information requested in the dialog that pops-up.
IMPORTANT: Group must be filled in, or it won't show for the Perform section
5) Click Add
6) Repeat steps 3 - 6 for any other networks that need to be added
7) Select Options option under Connect
8) Click Perform
9) If the network is in the drop down box, select it.
10) If not, click the Add button
10a) Select the network in the list that pops-up and press OK
11) Fill in the commands you want for that network
12) Repeat steps 9 - 12 for any other networks
13) Click OK