If you have already laid out an adequate single-point TA, you need not measure the course again.
You can establish a new TA having a radius of, say, 4 meters simply by figuring out how much is added and subtracted.
A single-point TA has the runners using a radius of 10 cm.
Your new TA of four meters radius will have the same 10 cm offset, but the runners' path is longer.
Simply figure the difference between the two paths and move the TA radius center toward the start so that the distance lost is equal to the distance gained. The only measurmeent needed is the short taping that records the shift of the TA center point.
No need to bike the whole course again. That is absolutely unnecessary and a waste of valuable time.