tallyho

Unfortunately I had to use Affinity Photo to do it as I needed to use the View > Studio > Info panel to constantly sample the colour to be changed for me to be able to accurately input the values into the Levels Adjustment.
Affinity Designer does not have a View > Studio > Info panel. But fortunately as the two programs work together just copying the Levels adjustment layer to Affinity Designer retained the values.
I did not try to do it just using Affinity Designer as since I paid for both programs I like getting my money's worth but someone else may see another accurate way to do it just using Designer.

Hard to advise without seeing the document/template but the Levels adjustment in the attached file should change the 1st rectangle (#7CC147) to the same colour as the second rectangle (#1DC021)
Copy just this adjustment layer to your template(?) at the top most layer and see if it adjusts all other colours as you want them.
 
 
colours.afdesign

Just for laughs I can get it to RGB (30:192:33) which is (1EC021) and the 1DC021 is RGB (29:192:33) using a HSL adjustment layer.
 
Why can't you just select all the vector parts that you need to be 1DC021 and just change them from the colour panel?
maybe a screen grab would help understand your dilemma a bit more.
Re adjusting other colours accordingly you mean a colour shift en masse 

Hi tallyho,
Welcome to the forums
There's currently no find and replace feature for fills in Affinity, nor do we have an adjustment layer that can automatically adjust colours based on one colour change. You will have to create separate recolour adjustments, masked to each colour you wish to change, or change the fills manually.
Is this a feature you have seen elsewhere? Simply it's not an adjustment type I've heard of before!