I don't know how to code an effect and I believe that it is a bit of a challenge. You could use python to code adding a transform effect with those parameters already defined, or you could append this metastrip plus effect fro another "master" blend file scene.
Here I have created a metastrip by adding a color effect (red) then pressing Ctrl-G. To this metastrip I added a transform effect and set the scale and x,y values. I also changed the blend type to "overdrop"
Next I selected the metastrip and its transform effect and duplicated them with Shift-D. I can place this duplicate metastrip anywhere on the timeline. Press the TAB key to step nside the metastrip and change the media.
Press the TAB key to get back out to the master sequence timeline, then you can drag the end handle of the metastrip to the correct new length.
Then you could split your screen to make a little FX bin on the side.
This is at timeline -0. In other words, you place a bunch of stuff outside the rendered timeline. Then you can select them no matter where you are in the edited timeline. They wont zoom or move unless you change it. I have also altered the color of that red strip in the other effect so that you can identify the one that you want to use, it may have different x,y offset values or scale etc.
Also you could enable the Addon Extra Sequencer Actions, then use it to copy the transform and blend type properties from your original effect to the others. It is a bit fiddly to select correctly. Make sure the master effect is the last one that you select.