You are right, once the font has been modified, there’s apparently no way to go back.
However, there’s a workaround. wxFormbuilder saves files with .fbp extension. These files contain pure xml that you can edit manually (before doing so, exit wxFormBuilder).
A button is described like this :
<object class="wxButton" expanded="1">
<property name="BottomDockable">1</property>
<property name="LeftDockable">1</property>
<property name="RightDockable">1</property>
<property name="TopDockable">1</property>
<property name="aui_layer"></property>
<property name="aui_name"></property>
<property name="aui_position"></property>
<property name="aui_row"></property>
<property name="best_size"></property>
<property name="bg"></property>
<property name="bitmap"></property>
<property name="caption"></property>
<property name="caption_visible">1</property>
<property name="center_pane">0</property>
<property name="close_button">1</property>
<property name="context_help"></property>
<property name="context_menu">1</property>
<property name="current"></property>
<property name="default">0</property>
<property name="default_pane">0</property>
<property name="disabled"></property>
<property name="dock">Dock</property>
<property name="dock_fixed">0</property>
<property name="docking">Left</property>
<property name="enabled">1</property>
<property name="fg"></property>
<property name="floatable">1</property>
<property name="focus"></property>
<property name="font"></property>
<property name="gripper">0</property>
<property name="hidden">0</property>
<property name="id">wxID_ANY</property>
<property name="label">This is my Button</property>
<property name="margins"></property>
<property name="markup">0</property>
<property name="max_size"></property>
<property name="maximize_button">0</property>
<property name="maximum_size"></property>
<property name="min_size"></property>
<property name="minimize_button">0</property>
<property name="minimum_size"></property>
<property name="moveable">1</property>
<property name="name">m_button1</property>
<property name="pane_border">1</property>
<property name="pane_position"></property>
<property name="pane_size"></property>
<property name="permission">protected</property>
<property name="pin_button">1</property>
<property name="pos"></property>
<property name="position"></property>
<property name="pressed"></property>
<property name="resize">Resizable</property>
<property name="show">1</property>
<property name="size"></property>
<property name="style"></property>
<property name="subclass">; ; forward_declare</property>
<property name="toolbar_pane">0</property>
<property name="tooltip"></property>
<property name="validator_data_type"></property>
<property name="validator_style">wxFILTER_NONE</property>
<property name="validator_type">wxDefaultValidator</property>
<property name="validator_variable"></property>
<property name="window_extra_style"></property>
<property name="window_name"></property>
<property name="window_style"></property>
</object>
You can see the font parameter is like the following when not edited :
<property name="font"></property>
You just have to find the problematic font parameter (use the button name or label) in your .fbp file and correct it manually.
Nicolas