Clearly if you just became aware of the mold and you notified them pursuant to the addendum you did nothing in violation of the lease. There is no way that you could alert anyone before you become aware of an issue.
Was the addendum language anything this http://realtyselectonline.com/forms/moldaddendum.pdf
As far as the liability (did the tenant or the landlord cause the mold) we would need to look at the cause of the mold.
If the tenant did nit cause the mold this would be the landlord's responsibility under Texas law http://www.legalmatch.com/law-library/article/landlords-duties-regarding-mold-in-texas.html
“The Texas Property Code §92.056
LANDLORD LIABILITY AND TENANT REMEDIES;
NOTICE TIME FOR REPAIR”
Landlords are required to repair certain conditions. Once informed of mold not caused by the tenant the Landlord must make a diligent effort to repair or remedy certain conditions when all of the following requirements are met under Texas Property Code Section 92.052”
Texas Property Code Section 92.052
Sec. 92.052. LANDLORD 'S DUTY TO REPAIR OR REMEDY.
A landlord shall make a diligent effort to repair or remedy a condition if:
the tenant specifies the condition in a notice to the person to whom or to the place where rent is normally paid;
the tenant is not delinquent in the payment of rent at the time notice is given; and
the condition materially affects the physical health or safety of an ordinary tenant.
Unless the condition was caused by normal wear and tear, the landlord does not have a duty during the lease term or a renewal or extension to repair or remedy a condition caused by:
a lawful occupant in the tenant's dwelling;
a member of the tenant's family; or
a guest or invitee of the tenant.
This subchapter does not require the landlord:
to furnish utilities
from a utility company if as a practical matter the utility lines of the company are not reasonably available; or
to furnish security guards.
The tenant's notice under Subsection (a) must be in writing only if the tenant's lease is in writing and requires written notice.
My concern for your is that the landlord would view the lapse in insurance as a breach of the lease and the mold would become a secondary issue.
Can you explain what caused the mold, where it is located and how you became aware of it?
If the mold is the landlord's responsibility you have several options
"Option #1) terminate the lease and move;
Option #2) file suit to obtain damages
and an order requiring the landlord to fix the problem (it's fast, easy and has fewer risks);
Option #3) have the problem repaired and deduct the cost from the rent (this is hard to do correctly, and most landlords file for eviction
for nonpayment anyway, which bad for your rental record even if you win);
Option #4) notify the city code inspector about the problem;"
More information on your remedies as tenant are located at this link