phpBB forbids modification of the main php files. If you want to change the data, you need to use the extension. But you are not in this case.
For the template, it is recommended to use the Template Template extension, especially when you need to add some new features. But you can change your template, especially in your case!
Here is a good practice:
Create a new spotlight to create a style
# General Information about youstyle name = mystyle copyright = © phpBB Limited, 2016 style_version = 3.1.10 phpbb_version = 3.1.10 # Defining a different template bitfield # template_bitfield = lNg= # Parent style # Set value to empty or to this style name # if this style does not have a parent style parent = prosilver
Copy / paste the viewforum.phtml template file , you want to change it in your new style directories and change it directly.
phpBB/styles/mystyle/template/viewforum_body.html
Use the admin panel to check your modification. When this is done, change the default template from prosilver to mystyle
Here is a good documentation on Inheritance Template
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