Power Query Custom replacer function

Hi,
Can someone help with information or direct me to post or blog re how the replacer function works in M ,

I have basic replace value ;

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which can be re written ;

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but to take a stage further and replace based on another column;

Table.ReplaceValue( Source,
each [Unit] ,
each if [Item] = "A" then [Unit] * 10 else [Unit] , Replacer.ReplaceValue, {"Unit"} )

But I cannot figure how to re write with 'custome replacer' , I have tried various such as ;

=

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Which I thought item = "A" then z = current valuue * 10 ?

Richard.

True, but it's also text for the 'replace condition' and it works fine, if you change it to number it still does not work.
my problem is with the syntax for a custom replacer.
rd,

Thanks, I have not had a chance to try this yet, I can find very little information on this so if you can point in direction of more information
pleaee do, i've found Rick de Groot has some very interesting / complex examples

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just in case you haven't seen it, most of if over my head.

Richard.

Thanks for the suggestion, but i was trying to avoid using the built in replacer function as it seems to have it's limitations.

Richard.

To deal with a condition over multiple columns, also just type in replacer does not really give much idea as to what it's doing.

=

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This is the question I asked answer by rory;

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Thanks again, yes working through it it and looking it makes perfect sense, how simple everything is once it's been pointed out by someone else.😊

Richard.