I'm trying to make new iron bars that can connect to my own blocks.

I can't use  rusty_iron_bars = new BlockPane();    because the constructor is protected.

I can't make my own new pane class because that loses access to the rendering.

 

I tried making a class that extends BlockPane, but canPaneConnectToBlock can't be overridden so I can't change that method to add my own blocks.

 

Is there any way of doing this?

You need to make a new pane class for yourself, but you also need to copy the corresponding renderer and put it in a blockrenderee of your own( just take the render id and select the corresponding render code from the if statements in the vanilla blockrenderer)

 

Then modify it. If you extend blockpane on the block you also allow other mods to connect to it which would do it this way.