[ndt]

"why should one assume changes in DNA goes on indefinitely and uniformly? "

Uniformly they do not, the rate mutations are based on many things from toxins and radiation to transcription errors, but standard rates can be calculated.

As for going on indefinitely, please tell me what would stop them. If you can answer that I'll nominate you for a noble prize because you have just cured cancer.

[flevit]

absence of evidence is not evidence of absence.
it is unknown.

that still provides no reason why it should be assumed to go on indefinitely especially with dogmatism.

not to mention these changes in DNA have yet to be demonstrated to add information to the genome. As opposed to tuning up/down existing information. (the loss of armor in the stickle back)