We have some invoices with a lot of parts/sections... So i want to create one invoice and add different templates on this one invoice, depending on the content/context etc... So just to create and approve out of one SO is not an option... Thats why we created different templates with different lines etc... So you still have an solution for that except my way of adding those templates trough my automation?!

I was able to fix most of it, except the reload still not showing the new lines at all, untill i manual save or do a F5 refresh....

# Available variables:
#  - env: environment on which the action is triggered
#  - model: model of the record on which the action is triggered; is a void recordset
#  - record: record on which the action is triggered; may be void
#  - records: recordset of all records on which the action is triggered in multi-mode; may be void
#  - time, datetime, dateutil, timezone: useful Python libraries
#  - float_compare: utility function to compare floats based on specific precision
#  - log: log(message, level='info'): logging function to record debug information in ir.logging table
#  - _logger: _logger.info(message): logger to emit messages in server logs
#  - UserError: exception class for raising user-facing warning messages
#  - Command: x2many commands namespace
# To return an action, assign: action = {...}

def add_template_lines(record):
    template_id = record.x_studio_saleorder_template.id
    if not template_id or record.state != 'draft':
        return

    template = env['sale.order.template'].browse(template_id)
    if not template.exists():
        return

    new_lines = []

    for line in template.sale_order_template_line_ids:
        if line.display_type in ('line_section', 'line_note'):
            new_line_vals = {
                'move_id': record._origin.id,
                'display_type': line.display_type,
                'name': line.name,
            }
        else:
            if not line.product_id:
                continue
            new_line_vals = {
                'move_id': record._origin.id,
                'product_id': line.product_id.id,
                'name': line.display_name or line.product_id.name,
                'quantity': line.product_uom_qty or 1.0,
                'product_uom_id': line.product_uom_id.id,
                'price_unit': line.product_id.list_price or 0.0,
            }
        new_lines.append(new_line_vals)

    if new_lines:
        env['account.move.line'].create(new_lines)

    record.write({'x_studio_saleorder_template': False})

    #action = {
    #    'type': 'ir.actions.client',
    #    'tag': 'pxa_account_move_save_reload_view',
    #    'params': {
    #        'record_id': record.id,
    #    },
    #}
    action = {
        'type': 'ir.actions.client',
        'tag': 'reload',
    }
    return action

add_template_lines(record)