Dear @gusspec
Ron's suggestion is good. If you wanted to stay at the Parametric Mode, the" Replace Face" command works exactly the same. You select "Create Form" then select the face and to convert. Be sure to click "Brep". after the conversion you click "Finish Form" and then select "Replace Face" from the "Modify" Menu. The original face is the source face, the newly created face is the Target Face.
The good thing about this mode is the T-Spline plane is still there. You can work on the light bulbs to show that or not. This operation can roll backwards and you can edit your the T-Spline Plane. I also suggested tools like creasing, uncreasing, insert edges, slide edges. The original "Source Face" is still there too. You can roll back on the timeline to edit as well. I was a bit against the Parametric Mode when they first changed to this feature but now I really like it and I just stay with this mode.
On the precision part, you can always limit yourself in your edit form. The good thing about edit form is you can select the area to be affected by your editing and the Falloff. You can also form a box around your model with the precise dimension you would limit your model. Sketch the box and I suggest you to right click on the lines and select to change them into Construcion Lines. They will change to dotted lines. You can also select that from the Sketch Tool Box that will come out. Easier to distinguish. Then you can edit your form not to exceed the boundary box.
The Direct Modeling mode is important to me too. After I created my model and when ready to be sent to mold designing/making, I always saved a Parametric Version of my file in the Fusion cloud and my own hard disk. I then "Stop Recording" and saved a DM version. I will delete the hidden files, and generate a smaller and cleaner stp file to mold designers/makers to build the molds.
Parametric Files seems to have a lot of hidden files inside and the resulting STP file could be too large. One thing good about Parametric Mode is the ability to roll back in time, edit something and what's after could be changed too. I said "could be" because not everything could be changed afterwards. Most of the things at the parametric mode could not be deleted otherwise there will be yellow icon on the timeline. If that happened, I will change to Direct Modeling mode.
Your file is not a very complicated file and could be relatively easy to modify. Play around with the commands and you will be able to do things the way you wanted.
One advice, copy and paste a few of your files in the cloud. Rename them to something like nnn v1., nnn v2 and so on. Just in case you made a mistake you can always have back up files available.
Have fun!
@Oceanconcepts Ron, Thanks for joining! Thanks for refreshing my mind in the DM mode. Oh by the way Ron, this is your old friend Kingson. I changed to MAS account two months ago due to problem in HK licensing.
Regards,
Kingson
PS Ron, "LuvMeSweet" is my registered trademarks in a few countries, thanks to Fusion360 that set me up in this business a few years' back!