how to change 'zero' position

This is a general quesiton about changing the 'zero' position during program operation. The machine is a Bridgeport BOSS converted to Linuxcnc. (the result is very impressive, thant you all for your efforts and your support.)
I am manually writing gcode. I am not using any CAD/CAM software. I am simply using a text editor to create and manage program codes.
My first project was circle based. I simply centered the part on the spindle, turned the power on and proceeded. The part and the coordinate system were aligned.
My second project is to machine a rectangular part from blanks. I will afix the part and determine the edges. Once that is complete the program will locate the spindle to the 'center'. At this time I would like to reset the coordinate system.
How can this be done? I believe this can be done using g5x codes. Is this the best way? Is it the only way?
Thank you in advance, Dan

To set offset for G54 from machine origin to X233.5 Y47

or

To set offset for G55 from actual position to X233.5 Y47

To set actual position ,G54 to zero

To set G54 X0 Y0 to machine origin, moves are then the same as G53 used,

I am shure there is a section in the documentation about G10 L2 and G10 L20

Thank you. This is a very helpful start. The machine is a Bridgeport BOSS. The project is to create a part program with the blank in an unknown position.
When I start the machine it starts in position x0 y0. When I zero of the part edges the x pos becomes v1 and y becomes v2. Will the following command set the operational offset to x0 y0?
G10 L20 P1 X0 Y0
I sort of understand the G10 command. I don't understand the fuction of L20 and P1 in this example.
(Follow up: I restarted Linuxcnc with the blank in the jig. I then cleared E-Stop and enabled machine power. This allowed positioning the table to zero - zero on the blank in the jig. I then 'homed' the axis. This cleared the x and y offsets. Is this an alternative? )

Sounds like you are trying to do the same thing I have been doing. Changing from the machines x0 y0 to a work piece x0 y0. I use G10 L2 P0 with the xy coordinates for the work piece x0 y0. To establish z0, I touch off each tool and record the number. An example would be G10 L2 P0 X3 Y2 Z-1.5
To change tools,
G53 G00 Z0
M9
G53 G00 X0 Y0
M0
(Press S to continue)
G10 L2 P0 X3 Y2 Z-1.6
G00 X Y start position
M8
G00 Z0

I use M8 M9 because the typical M code s to turn the spindle on/off don't work. Turns the spindle on but not off.
Anyway, this is how I handle my offsets.

i not understand good english, but how make little manual work, need move manual bit top off work piece, and then make this Z zero point and start example "linuxcnc" text or other program first starting, i has try many time make zeroing. first doing all home, then manual move bit top off workpiece, then start run linuxcnc text carwing, BUT alltime start same . bit go up and run text g-code to air far up to workpiece.
why ? why not start run carving to wood, how move thats bit go down top off workp, and then go make text to wood how move position right ??? i not understand, i has try many time carving my first text or own manual writing G-code but no go to make in wood thats, only far up to wood run bit. sorry my english not good. step by step help how i start do first carwing job. i need make piece at belt tightening frame part both Y axis have timing same not losses steps if somethink have wrong. both treath must run whit belt same position alltime. i have 2 motor at Y axis, need build timing sure same belt connection pieces but need first understand how run bit to wood not only up far wood and move only air.