ROMPatcher Plus is an application with multiple application resources,You have to install the application first, this will cause you to install any application (including unsigned), no certificate error. Besides the install server the ROMPatcher Plus connects the patch with various functions to customize,

ROMPatcher Plus V3.1

fix mistakes and change functions of your Symbian.

New in ROMPatcher Plus V3.1

There are many new features in itwhich are not available in the previous versions.

Lite version is already signed, you need not sign it with a DevCert.
InstallServer.rmp + Patch has been updated.
This ROMPatcher Plus version is compatible with all the 3rh, 5th, S^3 devices.
It supports for compiled patches.
It can dump the whole ROM content to file \romdumpplus.dmp.
It can dump the Super-Page content to file \superpage.dmp.
It has full support for DomainSrv.exe autostart, with Recovery Fault.
New commands i.e. ord_rel, ord_snr are introduced which allow to patch DLL using ordinal
RomPatcherAuto.exe has been renamed to RPPAuto.exe for better compatibility with Samsumg Omnia auto start.
It can be integrated in cooked ROM firmware.
And many more.

How to install ROMPatcher Plus V3.1 for Symbian^3

There are two ways I mentioned here to install the ROMPatcher Plus V3.1.

If your phone has been hacked to allow installation of unsigned .sis then install RomPatcher Plus_3.1.sis
If your phone has not been hacked yet, check out the file "LiteVersion\ReadMe.txt"