problem update replace attribute

Hi,
I want to replace an attribute element and I don’t know how to do it. With normal elements it works but with attributes I don’t know what more to test.
This is my query to see it more clearly.

It works in this case:

update let $a:= input()/DVD/Media/DMS1:ClipFramework[last()]
do (
replace $a/extension_rp210Elements:IsOptional/text() with “false”
)

With attributes not works:

update let $a:= input()/DVD/Media/DMS1:ClipFramework[last()]
do (
replace $a/@rp210Elements:InstanceUID/text() with “21.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00”
)

Maybe with attributes(@) it is necessary any special command.
If someone could help me I will be very grateful.
Thanks a lot,
Diego

See if this syntax will work for you:

update let $a:= input()/DVD/Media/DMS1:ClipFramework[last()] 
do ( 
replace $a/@rp210Elements:InstanceUID with attribute rp210Elements:InstanceUID {"21.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00" }
) 

Thanks a lot, it works perfectly.
Regards,
Diego