Try using xpath either you have to replace or inserting inside the layout.
For example:

<template name="websitecustom" id="website.custom" inherit_id="website.homepage">
        <xpath expr="//div[@id='wrap']" position="replace">
 <p> Insert here </p>

      </xpath>
    </template>

Hi,

If you are looking to apply changes inside the odoo views, like form, tree, pivot etc, you can inherit those views apply changes like changing labels, adding new fields, hiding existing fields etc. For this, just you need to create a new module inherit the corresponding view and apply changes using the xpath in the inherited view.

Sample:

See the sample of adding a new field in existing view in the sales module,

<record id="sale_order_inherit" model="ir.ui.view">
    <field name="name">sale.order.inherit</field>
    <field name="model">sale.order</field>
    <field name="inherit_id" ref="sale.view_order_form"/>
    <field name="arch" type="xml">
        <field name="partner_id" position="after">
            <field name="new_field"/>
        </field>
    </field>
</record>

Another sample of making an existing field invisible,

<record id="sale_order_inherit" model="ir.ui.view">
    <field name="name">sale.order.inherit</field>
    <field name="model">sale.order</field>
    <field name="inherit_id" ref="sale.view_order_form"/>
    <field name="arch" type="xml">
        <field name="payment_term_id" position="attributes">
            <attribute name="invisible">1</attribute>
        </field>
    </field>
</record>

If you are new to odoo, have a look at this explaining the same: How To Inherit And Add New Fields To Existing Views

Thanks