UJ_VALIDATION - Shared driver dimension between models

Question

Hello Experts,
I'm having a little problem and I would like to know if you could lend me a hand to find a solution. The situation is as follows:
We are using BPC 10 NW (801 SP3) where we have a planning environment with 3 models, plus a rate model. From this 3 models, two (Mod_1 and Mod_2, for reference) are almost identical but we keep them separated because the set of users, data access profiles and administration tasks needs to be independent from one another and this was defined by the business users. One of this administration tasks happens to be data validation, for which we use UJ_VALIDATION. The validations that need to be defined in both models basically states that for a set accounts (driver dimension), for example, the ENTITY member should not be "NA", but this is not necessarily required for Mod_2 (same driver dimension) in which we don't want to have a validation in the same acoounts. For example:
Mod_1 (ACCOUNT driver dimension)
Rule 01
ACCOUNT = 410, 420, 430
COSTCENTER <> NA
Rule 02
ACCOUNT = 510, 520
ENTITY <> NA
Mod_2 (ACCOUNT driver dimension)
Rule 01
ACCOUNT = 430, 440
COSTCENTER <> NA
Rule 02
ACCOUNT = 530, 540, 550
ENTITY <> NA
Rule 03
ACCOUNT = 410, 420, 430
PRODUCT <> NA
When we tried to set this validations we found that the rules itself are linked to the driver dimension and could not be defined for each model independently. Since the same accounts are used for both models the definition is being quite troublesome. So, here comes the questions:
Is the UJ_VALIDATION working as expected? I mean, is it normal that the rules are defined at the driver dimension level and can not be defined for each model using the same driver dimension and a different set of rules for each?
If the answer to question 1 is "Yes, it's working as expected", what's the reason behind it?
What are the options available to cover this requirement? We hope that using a BAdI is our last resort as it's not very user friendly and this rules are changed constantly by the business users.
Thank you very much for your time. I hope that you could help me to find a solution.

Answer 1

Vadim, thanks for your reply. I see you often lending a hand to people with questions and it's much appreciated.
Regarding your answers I have a few questions. I hope you don't mind:
Too bad
Ok, it's unusual to have two similar models just for administration and security instead of one. But what happens if I have two or more very different models and I need to use the same driver dimension for each. There is not a 'standard' solution that UJ_VALIDATION could provide and keep the rules independent from one another? My situation may be a particular case, but in a general scenario I still think that keeping the rules linked to the driver dimension instead of the model itself limits it's functionality and I would like to understand better the reason behind this decision, if there's any.
Do you know where I can find a guide where it shows step by step how to implement UJ_VALIDATION_RULE_LOGIC BAdI? I don't have much knowledge in ABAP nor in BAdI implementation, so I'll need a lot of help to make this work, heh. I know that I need to learn both sometime and this may be the perfect situation to step into it.
Thanks again for your time!
Best regards,
Joaquin.