The use of "conservative" in your sentence is correct and does have the meaning of "erring on the safe side" especially in safety regulations. These types of guidelines, more often than not, add to the cost of a project since many different scenarios need to be taken into account.

Similar words you might use are

The guidelines are quite strict, leading to costly 'over-design'
The guidelines are very prescribed, leading to costly 'over-design'

although both words do not have the implies meaning of "erring on the safe side", they do describe how a regulating body would define their requirements.

From you edit, you could use

The guidelines leave lots of room for error, leading to costly 'over-design'
The guidelines are over specified, leading to costly 'over-design'

both sentences have the meaning that the specified loadings are much more than necessary.

The use of "conservative" in your sentence is correct and does have the meaning of "erring on the safe side" especially in safety regulations. These types of guidelines, more often than not, add to the cost of a project since many different scenarios need to be taken into account.

Similar words you might use are

The guidelines are quite strict, leading to costly 'over-design'
The guidelines are very prescribed, leading to costly 'over-design'

although both words do not have the implies meaning of "erring on the safe side", they do describe how a regulating body would define their requirements.

From your edit, you could use

The guidelines leave lots of room for error, leading to costly 'over-design'
The guidelines are over specified, leading to costly 'over-design'

both sentences have the meaning that the specified loadings are much more than necessary.