What are some ways to transition from additive to multiplicative(or vice-versa) changes in time-series quickly?

Let’s say I have a variable x and as time progresses, I want to update the value of x in additive/multiplicative manner using some attributes.

At t=t, new_x = x * some_percentage or new_x = x + some_absolute_number.

Is there some way to transition from additive change to multiplicative change or vice-versa and the number by which we can? It’s fine if we focus only on one of the additive or multiplicative by reactively changing the percentage_increase or absolute_change.

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A toy example task (hypothetical)

For a salary of 100k, an increase of 50% is significant but for a salary of 100(could be pocket money of some child), a 50% increase might not be enough. When we are discussing a smaller number of salaries, we need to increase the salary by absolute number. For a salary of 100, we can increase it by 70 to make it 170)

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Are there any ways or literature to handle this which can adapt quickly?