As a GM myself, one of the first things to be modified in any store bought 'canned module' I ever owned would be the difficulty level of skill checks (open locks, disarm traps, spot hidden objects, etc), and usually the encounters (number appearing, HD, HP, items/loot carried). My ultimate goal when running an adventure has always been to maintain a challenge for my players, based on their unique strengths and weaknesses as a group, and to reward them appropriately for their efforts. I wrote Ryubix Manor to be as GM friendly to modification as possible, and to that end I implemented two features:
First, I use two acronyms throughout Ryubix Manor. AST (Appropriate Saving Throw) and ASC (Appropriate Skill Check). As an example:
The battered trunk is locked (ASC to open) with a poison-needle trap (6-36 HP damage, AST to resist)
Rather than set a threshold number that might be inappropriate to your style of play (too easy or too hard) or meaningless to your rule system (percentages for AD&D, DCs for Pathfinder, number of successes or resistance rolls) I leave the specific number to your discretion. The module is yours, after all, who better than you as the GM to decide how challenging the situation is for your players?
Second, as described in the first FAQ above, creature encounter descriptions are kept to a minimum in the GM notes. This was done to maintain the greatest amount of flexibility for the GM. A spider is a spider is a spider, but the specific statistics for them vary from rule set to rule set. All creatures encountered in Ryubix Manor can be found in the OGL system, simply because there had to be a common basis to draw from. For those GMs running OGL or Pathfinder systems, I have included Encounter Bestiaries (formatted stat/ability blocks) as a free download. These 'default' stats for the creatures are, as always, open to GM modification. With few exceptions, the monster encounters are what one would expect in a haunted house--ghosts, ghouls, skeletons, zombies, a vampire or two, and so on. I can't think of any D&D type game that doesn't include these creatures. (although I'm sure someone will inform me of one after I post this FAQ)
Ryubix Manor is comprised of atmospheric room descriptions for players, combined with GM notes of each area revealing 'the whole picture'. The ability to plug a variety of Sword and Sorcery type rule sets into the Manor would define it as 'system agnostic'