How to make changes to a human person's DNA actually be expressed in the individual's phenotype

A flaw very often pointed out in your run of the mill genetic terror story is the instant effect of genetic changes.

What would it take for a specific change in the specimen to actually appear (near) instantly?

Example:

I (well not really me, you know right) want to engineer a human individual to grow an additional finger.

• Assume perfect knowledge required to engineer the required genetic code.
• Injection vector etc. is all sorted out.
• Assume high-tech tissue regeneration technology, which could regenerate limbs, but not a complete brain.

My genetic information is now within the specimen. From my (simple) understanding I have now changed the blueprint, the building plan for this individual, right?

• Do I have to, say chop the hand off, and let it regrow, according to the new genetic code?
• Will it grow itself somehow?
• Can this change only occur in the next generation (offspring) and how to avoid this.

EDIT: This is not about changing the code itself, its about making the changes actually appear

FURTHER CLARIFICATION: Assume an advanced intelligence injecting precise dna snippets into humans. This is my major handwave.
Now I want to reduce -if at all possible- the following handwaves as much as possible, namely the circumstances under with the introduced changes would actually show themselves.

I changed from science-based to reality-check because the answer requires handwaves in its pre-condition.

posted over 6 years ago

System‭

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