Is it safe to add sql indexes?

Configuration
1

i just moved from sqlite to mysql. i have some sensors that uses sql query to present my data. is it safe to add indexes to the tables? will it be ok for future upgrades?

2

I looked in my db and it already has a number of indexes on the tables. What indexes were you thinking about adding?

Keys from states: PRIMARY KEY (state_id),
KEY event_id (event_id),
KEY ix_states_last_updated (last_updated),
KEY ix_states_entity_id_last_updated (entity_id(191),last_updated),

keys from events: PRIMARY KEY (event_id),
KEY ix_events_event_type (event_type),
KEY ix_events_time_fired (time_fired)