I'm taking a bit of a stab in the dark here but it might be helpful anyway.

I've never come across the terms "verfahrensleitend / verfahrensabschließend" when I practiced law (and only seem to vaguely remember these terms as having s.th. to do with the procedural law in relation to the German Constitutional Court), but then again I've never worked as a patent attorney.

I'm assuming that these terms refer to opposition proceedings before a patent office rather than a patent court ("Zwischenbescheid = interim notice" suggests that it is the office rather than the patent court; also, the Einspruchsverfahren before the patent office is typically concluded by way of a Beschluss).

"Verfahrensleitend" seems to refer to setting the boundaries (parameters) for any further proceedings in a particular case, requiring the authorities (or even the court) to comply with certain decisions (that were not necessarily made by a court but by government authorities), therefore binding the patent office to a certain degree.

("Die angegriffene Weisung ... hat einen verfahrensleitenden Inhalt, denn sie gibt für die Durchführung des Genehmigungsverfahrens dem Landesminister bestimmte Rechtsauffassungen zum Bestandsschutz bereits erteilter Teilgenehmigungen und zur Bindungswirkung des vorläufigen positiven Gesamturteils zur Beachtung auf.")

"Verfahrensabschließend" is comparatively simple and refers to the conclusion / finalisation of the proceedings, eg "verfahrensabschließender Bescheid" would translate to "notice concluding / finalising proceedings".

Suggested translation for your sentence:
"... to issue an interim notice that sets the boundaries [parameters] for any further proceedings prior to making a decision with regard to the opposition lodged."

The translation of "Es wird beantragt" depends on the overall context.