I understand why you don't want to use a default value, per RG's suggestion. However, if you want to set a bunch of values without using defaults, you're going to have to do that
somehow, i.e., "an if statement for every field".
I would probably go with a statement in the BeforeUpdate event of each relevant control that goes iif(nz(me.value,"")="","888",me.value).
Alternately, you could put some code behind the BeforeUpdate event of the form itself that checks all the relevant controls and sets them to 888 if they're blank using a series of statements similar to the above. You still have to write the same number of statements, they're just all in one place.
EDIT: The second approach is the correct way. See Pat Hartman's insights below.
For more info on Nz (per your original question), check Access help and read
this article.
--Iffy Mac
EDIT: I agree with RG, if you're using 888 to stand for "no data", then just use nulls.
Also, the change of 888 for blank values in existing records can be accomplished with an UPDATE query. Check Access help.