Is it possible to add one custom button of your add-in to the existing tab at the ribbon and one to

[etceterad]

I'm trying to add 2 buttons to the different tabs in Word via XML Manifest, but now for me, it seems to be impossible. That's all because I can't add OfficeTab and CustomTab in ExtensionPoint with xsi:type="PrimaryCommandSurface". Are there any other possibilities to implement such an idea?

[#2]

It is not really clear what you are wanting to do. However, see the following page of Greg Maxey's website
https://gregmaxey.com/word_tip_pages/customize_ribbon_main.html
The following xml code adds a custom button to the Mailings tab of the ribbon

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui">
<ribbon>
<tabs>
<tab idMso="TabMailings">
<group id="customGroup" label="Merge Special" insertAfterMso="GroupMailMergeFinish">
<button id="customButton" label="Merge to Word and PDF" size="large" imageMso="ExportToVCardFile" onAction="MergetoWordPDF" />
</group>
</tab>
</tabs>
</ribbon>
</customUI>

[#3]

Thanks for the advice, but it's probably not the thing that I was looking for.
As I write in the description I want to add 2 custom buttons of my add-in - one on the existing "Home" tab and another one on the custom tab. Additionally, I'm using the new syntax of XML Manifest, such as described here: https://docs.microsoft.com/ru-ru/office/dev/add-ins/develop/add-in-manifests?tabs=tabid-1

[#4]

I beg to differ. To add a custom button to the Home tab, you must use the Custom UI Editor and with it, you can also create a custom tab to which you can add a other custom (or built-in) buttons.

[#5]

The custom button of my custom Word add-in, which I'm provided to Word locally via XML Manifest. I've attached a link to the previous answer about the Manifests. You can manage the placement of your custom content only with such XML Manifests. If you want to add your custom button to the existing tab you need to use <OfficeTab> in Manifest and if you want to add it on the custom tab at the ribbon you need to use the <CustomTab>, but the documentation says, that you can't use both tags at the same time.

[#6]

@etceterad 

The code in the attached Custom UI XML Code.jpg adds a Custom Group to the Home tab of the ribbon that contains the mixture of Native and Custom buttons that appear in the File Actions Section of the Home tab of the ribbon as shown in the attached Custom Button on Home Tab.jpg.  AT THE SAME TIME, it also adds the custom Merge Tools tab to the ribbon that contains the buttons shown in the attached Merge Tools Tab.jpg