Can I file a preliminary objection to the modifing of the exsisting order.

They are normally reserved for responses to civil complaints.  Indeed, there may not even be a procedure for the court to resolve it.  One reason is that petitions to modify custody can be filed at any time by either party.  I cannot conceive of a basis for filing POs.  That differs from a complaint for custody in which I filed POs once based on the parties living together.  That is a jurisdictional issue.  It may be simplest to address any legal issues you wanted to raise by the POs before the master, conciliator, or judge, depending on what county you are in. I hope that answers your questions but feel free to call or e-mail me on a free initial basis.